Zoom lens having an image stabilizing function

ABSTRACT

A zoom lens is disclosed comprising, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of negative refractive power, a fifth lens unit of positive refractive power and a sixth lens unit of negative refractive power, wherein, during zooming from the wide-angle end to the telephoto end, the air separations between the i-th and (i+1)st lens units are made to vary properly and the ratio of the focal length of the fourth lens unit to the longest focal length of the entire system is made to have a proper value. In particular, a zoom lens is disclosed wherein the second lens unit is made to decenter to stabilize the image.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to zoom lenses of the telephoto typesuited to 35 mm cameras, video cameras or electronic still cameras and,more particularly, to zoom lenses having four to six lens units intotal, of which certain ones are movable for zooming, and having as higha range as 4 or thereabout with maintenance of a high opticalperformance throughout the zooming range, while still permittingimprovements of the compact form of the entire system.

[0003] 2. Description of the Related Art

[0004] For the photographic cameras and video cameras, there have beendemanded zoom lenses of high range with high optical performance. Ofthese, the telephoto type has been proposed in a wide variety ofmulti-unit zoom lenses in which three or more lens units are movable forzooming.

[0005] For example, a 3-unit zoom lens of plus-minus-plus powerarrangement in this order from the object side, a 4-unit zoom lens ofplus-minus-plus-plus power arrangement, another 4-unit zoom lens ofplus-minus-minus-plus power arrangement, a 5-unit zoom lens ofplus-minus-plus-minus-plus power arrangement, another 5-unit zoom lensof plus-minus-plus-plus-minus power arrangement, and many others havebeen proposed, wherein a plurality of lens units are moved to effectzooming.

[0006] Since, in these 3-unit, 4-unit and 5-unit zoom lenses, two ormore lens units contribute to a variation of the focal length, so thatthe requirements of minimizing the bulk and size of the entire lenssystem and of obtaining a desired zoom ratio can be fulfilled at once.

[0007] Still another proposal for using six lens units has been made inJapanese Laid-Open Patent Application No. Hei 4-186212. With this 6-unitzoom lens of plus-minus-plus-minus-plus-minus power arrangement in thisorder from the object side, the zooming range is increased to as high as10.

[0008] In general, for the zoom lenses, it is desired not only toimprove the compact form of the entire lens system but also to extendthe zooming range (increase the zoom ratio). To achieve a great increaseof the zooming range, the number of those lens units which contribute tothe variation of the focal length may be increased. In addition, therefractive power of every lens unit may be increased to strengthen thezooming effect in some cases. In other cases, the movement of each ofthose lens units which contribute to the variation of the focal lengthmay be increased.

[0009] In the former case, however, to maintain good stability ofaberration correction throughout the zooming range, it becomes necessaryto increase the number of constituent lenses, giving rise to a difficultproblem of improving the compact form of the entire lens system.

[0010] In the latter case, to allow full zooming movements, the airseparations have to be much increased. This leads to elongate thephysical length of the complete lens. Particularly in a case where thelens units move in complicated relation, the mounting mechanism for themovable lens units becomes very elaborate, giving rise to a difficultproblem of improving the compact form of the entire lens system.

[0011] Meanwhile, there have been previous proposals for preventing aphotographed or picked-up image from shaking. Optical systems havingsuch a capability, or image stabilizing optical systems, are disclosedin, for example, Japanese Laid-Open Patent Application No. Sho 50-80147,Japanese Patent Publication No. Sho 56-21133 and Japanese Laid-OpenPatent Application No. Sho 61-223819.

[0012] In Japanese Laid-Open Patent Application No. Sho 50-80147, a zoomlens has two afocal zooming sections, wherein letting the angularmagnifications of the first and second sections be denoted by M1 and M2,respectively, these sections are made to move in such relation thatM₁=1−l/M₂ is kept and at the same time the second zooming section isheld in fixed spatial alignment with the original line of sight axis.The shaking of the image is thus corrected to achieve stabilization ofthe zoom lens against small angle deviation thereof from a desired lineof sight.

[0013] In Japanese Patent Publication No. Sho 56-21133, vibrations ofthe optical instrument are sensed by a detector. In response to itsoutput signal, part of the optics deflects to a direction so as tocompensate for accidental displacement of the instrument, thus achievingstabilization of an image in space.

[0014] In Japanese Laid-Open Patent application No. Sho 61-223819, aphotographic system has a variable angle prism of the refraction typearranged at the frontmost position. As the housing containing thephotographic system vibrates, this prism varies its apex angle todeflect the image. Thus, the image is stabilized in space for shooting.

[0015] Besides these, there are Japanese Patent Publications Nos. Sho56-34847 and Sho 57-7414, in which an optical member is arranged in partof the photographic system to be held in fixed spatial alignment withthe line of sight. As vibrations occur, this optical member and itsmating one generate a prism that deflects image light rays. A stabilizedimage is thus obtained on the focal plane.

[0016] Another available method is to utilize an acceleration sensor todetect vibrations of the housing of the photographic system. A lens unitconstituting part of the photographic system is made to rotate in thedirections perpendicular to an optical axis so that the image isstabilized against jiggles or oscillations at the focal plane.

[0017] In general, for the type of photographic system in which one lensunit is made to vibrate in such a way as to prevent the image fromshaking, the operating mechanism for image stabilization is required tohave capabilities that the tolerable shaking of the image to correct islarge enough, that the movement or rotation of that lens unit (shiftablelens unit) is small relative to the oscillation of the image, and thatthe driving means is small in size and light in weight.

[0018] The shiftable lens unit, when decentering, produces decenteringcoma, decentering astigmatism, decentering chromatic aberrations anddecentering curvature of field aberrations. If these aberrations arelarge, the image is caused to blur, although the shaking of the image iscorrected. For example, if large decentering distortion is produced, theimage shift in the paraxial zone becomes appreciably different from thatin the marginal zone. For this reason, if the paraxial zone alone istaken into consideration in controlling the decentering of the shiftablelens unit to correct the shaking of the image, it is in the marginalzone that a similar phenomenon to the shaking of the image takes place,causing the optical performance to lower objectionably.

[0019] In short, for the zoom lenses having the image stabilizingfunction, it is required that when the shiftable lens unit is moved inorthogonal directions to the optical axis to the decentered position,the amount of decentering aberrations produced is small so the loweringof the optical performance is little and that the required amount ofmovement of the shiftable lens unit for correcting the equivalentshaking of the image is small, in other words, the so-called decentersensitivity (ratio of the corrected amount, Δx, of shaking of the imageto the unity of amount of movement ΔH, or Δx/ ΔH) is large.

[0020] According to the prior art, however, the image stabilizingoptical systems of the type using an optical member as arranged,regardless of vibrations, to be held in fixed spatial alignment with theline of sight, are not suited to be used in instruments of small sizeand light weight, because this optical member is difficult tooperatively support-and because such optical systems are difficult torealize in compact form. Another type of image stabilizing opticalsystem using a variable angular prism as arranged in the frontmostposition, though having a merit that, when correcting the shaking, alldecentering aberrations except chromatic ones are produced to almostnothing, has problems that the driving members become large in size andthat the decentering chromatic aberrations produced from the prism aredifficult to correct with ease.

[0021] Yet another type of image stabilizing optical systems using onelens unit of the photographic optical system for decentering purposes isconsidered to be amenable to the technique of minimizing the size of theinstrument by proper selection and arrangement of the decentering lensunit. However, there is a difficult problem of simultaneously fulfillingthe requirements of well correcting all the aberrations produced bydecentering, namely, decentering coma, decentering astigmatism anddecentering curvature of field and of realizing reflection of thesufficiently small amount of decentering movement to a sufficientlygreat effect of stabilizing the image.

SUMMARY OF THE INVENTION

[0022] The present invention makes up a zoom lens from six lens units ofspecific refractive powers in total and sets forth proper rules for therefractive powers of all the lens units and for the relation in whichthe lens units move to effect zooming. Based on these rules, the numberof constituent lenses is reduced to insure that the physical length ofthe complete lens is shortened in such a manner that a high opticalperformance is maintained over the entire zooming range. It is,therefore, an object of the invention to provide a zoom lens of thetelephoto type having a range of about 4 with the image aberrationsimproved.

[0023] Another object of the invention is to provide a zoom lens havingan image stabilizing function and good optical performance. To this end,the zoom lens of the character described above is used as the base. Inapplication to this zoom lens, the method of correcting shaking of theimage is by moving part of the zoom lens, or the shiftable lens unit indirections perpendicular to an optical axis. To this purpose, as theshiftable lens unit, a one of small size and light weight is selected touse. In addition, its small decentering movement is reflected to correctlarge amplitude of shaking of the image. Furthermore, as the shiftablelens unit moves to parallel decenter, any of the decentering aberrationsdescribed before is produced to a smaller amount than was heretoforecommon.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIGS. 1(A), 1(B) and 1(C) are lens block diagrams of a numericalexample 1 of the invention.

[0025] FIGS. 2(A), 2(B) and 2(C) are lens block diagrams of a numericalexample 2 of the invention.

[0026] FIGS. 3(A), 3(B) and 3(C) are lens block diagrams of a numericalexample 3 of the invention.

[0027] FIGS. 4(A), 4(B) and 4(C) are graphic representations of thevarious aberrations of the numerical example 1 of the invention.

[0028] FIGS. 5(A), 5(B) and 5(C) are graphic representations of thevarious aberrations of the numerical example 2 of the invention.

[0029] FIGS. 6(A), 6(B) and 6(C) are graphic representations of thevarious aberrations of the numerical example 3 of the invention.

[0030] FIGS. 7(A), 7(B) and 7(C) are lens block diagrams of a numericalexample 4 of the invention.

[0031] FIGS. 8(A), 8(B) and 8(C) are lens block diagrams of a numericalexample 5 of the invention.

[0032] FIGS. 9(A), 9(B) and 9(C) are lens block diagrams of a numericalexample 6 of the invention.

[0033] FIGS. 10(A), 10(B) and 10(C) are lens block diagrams of anumerical example 7 of the invention.

[0034] FIGS. 11(A), 11(B) and 11(C) are graphic representations of thevarious aberrations of the numerical example 4 of the invention.

[0035] FIGS. 12(A), 12(B) and 12(C) are graphic representations of thevarious aberrations of the numerical example 5 of the invention.

[0036] FIGS. 13(A), 13(B) and 13(C) are graphic representations of thevarious aberrations of the numerical example 6 of the invention.

[0037] FIGS. 14(A), 14(B) and 14(C) are graphic representations of thevarious aberrations of the numerical example 7 of the invention.

[0038]FIG. 15 is a schematic diagram of the paraxial refractive powerarrangements of a numerical example 8 of a zoom lens of the invention.

[0039] FIGS. 16(A), 16(B) and 16(C) are lens block diagrams of thenumerical example 8 of the invention.

[0040]FIG. 17 is a schematic diagram of the paraxial refractive powerarrangements of a numerical example 9 of a zoom lens of the invention.

[0041] FIGS. 18(A), 18(B) and 18(C) are lens block diagrams of thenumerical example 9 of the invention.

[0042] FIGS. 19(A) and 19(B) are graphic representations of theaberrations of the numerical example 8 of the invention in thewide-angle end with an image respectively in the reference state and ina corrected state from the vibration of 1 degree.

[0043] FIGS. 20(A) and 20(B) are graphic representations of theaberrations of the numerical example 8 of the invention in a middleposition with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0044] FIGS. 21(A) and 21(B) are graphic representations of theaberrations of the numerical example 8 of the invention in the telephotoend with an image respectively in the reference state and in a correctedstate from the vibration of 1 degree.

[0045] FIGS. 22(A) and 22(B) are graphic representations of theaberrations of the numerical example 9 of the invention in thewide-angle end with an image respectively in the reference state and ina corrected state from the vibration of 1 degree.

[0046] FIGS. 23(A) and 23(B) are graphic representations of theaberrations of the numerical example 9 of the invention in a middleposition with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0047] FIGS. 24(A) and 24(B) are graphic representations of theaberrations of the numerical example 9 of the invention in the telephotoend with an image respectively in the reference state and in a correctedstate from the vibration of 1 degree.

[0048]FIG. 25 is a diagram to explain the correction of decenteringaberrations according to the invention.

[0049] FIGS. 26(A) and 26(B) are diagrams to explain the correction ofdecentering aberrations according to the invention.

[0050] FIGS. 27(A), 27(B) and 27(C) are lens block diagrams of anumerical example 10 of the invention.

[0051] FIGS. 28(A), 28(B) and 28(C) are lens block diagrams of anumerical example 11 of the invention.

[0052] FIGS. 29(A), 29(B) and 29(C) are lens block diagrams of anumerical example 12 of the invention.

[0053] FIGS. 30(A) and 30(B) are graphic representations of theaberrations of the numerical example 10 of the invention in thewide-angle end with an image respectively in the reference state and ina corrected state from the vibration of 1 degree.

[0054] FIGS. 31(A) and 31(B) are graphic representations of theaberrations of the numerical example 10 of the invention in a middleposition with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0055] FIGS. 32(A) and 32(B) are graphic representations of theaberrations of the numerical example 10 of the invention in thetelephoto end with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0056] FIGS. 33(A) and 33(B) are graphic representations of theaberrations of the numerical example 11 of the invention in thewide-angle end with an image respectively in the reference state and ina corrected state from the vibration of 1 degree.

[0057] FIGS. 34(A) and 34(B) are graphic representations of theaberrations of the numerical example 11 of the invention in a middleposition with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0058] FIGS. 35(A) and 35(B) are graphic representations of theaberrations of the numerical example 11 of the invention in thetelephoto end with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0059] FIGS. 36(A) and 36(B) are graphic representations of theaberrations of the numerical example 12 of the invention in thewide-angle end with an image respectively in the reference state and ina corrected state from the vibration of 1 degree.

[0060] FIGS. 37(A) and 37(B) are graphic representations of theaberrations of the numerical example 12 of the invention in a middleposition with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

[0061] FIGS. 38(A) and 38(B) are graphic representations of theaberrations of the numerical example 12 of the invention in thetelephoto end with an image respectively in the reference state and in acorrected state from the vibration of 1 degree.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0062] Numerical examples 1 to 3 of zoom lenses of the invention areshown in the longitudinal section views of FIGS. 1(A), 1(B) and 1(C)through FIGS. 3(A), 3(B) and 3(C), respectively. The aberrations of thezoom lenses of the numerical examples 1 to 3 are shown in FIGS. 4(A),4(B) and 4(C) through FIGS. 6(A), 6(B) and 6(C). Of the section views,the ones of the numbers with suffix (A) are in the wide-angle end, theones of the numbers with suffix (B) in a middle position and the ones ofthe numbers with suffix (C) in the telephoto end.

[0063] Referring to these figures, the zoom lens comprises, from frontto rear, a first lens unit L1 of positive refractive power, a secondlens unit L2 of negative refractive power, a third lens unit L3 ofpositive refractive power, a fourth lens unit L4 of negative refractivepower, a fifth lens unit L5 of positive refractive power and a sixthlens unit L6 of negative refractive power. SP stands for a stop and IPfor an image plane. The arrows indicate the loci of motion of the lensunits when zooming from the wide-angle end to the telephoto end.

[0064] In the present embodiment, the lens units L1 to L6 are madeselectively movable for zooming, wherein the selection is specifieddifferently from item to item. For every one of these zoom lenses, aszooming goes from the wide-angle end to the telephoto end, the selectedones of the lens units move axially in such relation that the separationbetween the first and second lens units increases, the separationbetween the second and third lens units decreases, the separationbetween the third and fourth lens units increases, the separationbetween the fourth and fifth lens units decreases and the separationbetween the fifth and sixth lens units decreases.

[0065] In other words, letting the separations between the i-th and(i+1)st lens units for the wide-angle end and the telephoto end bedenoted by DiW and DiT, respectively, the lens units are made to move insuch relation as to satisfy the following conditions:

D1W<D1T

D2W>D2T

D3W<D3T

D4W>D4T

D5W>D5T

[0066] An additional condition to satisfy is:

0.3<|f4/fT|<10.0  (1)

[0067] where f4 is the focal length of the fourth lens unit and fT isthe longest focal length of the entire system. When these conditions aresatisfied, the effect of varying the focal length is shared in goodbalance by all the lens units, thereby making it easy to extend thezooming range while still maintaining a shortening of the total lengthof the entire system to be achieved. Incidentally, the stop SP is madeto move in unison with the third lens unit.

[0068] In the zoom lens of the invention, for the wide-angle end, thefirst and second lens unit are positioned so closely that their combinedrefractive power becomes negative. The third and fourth lens units arealso closely positioned. Further, the third lens unit and those thatfollow have their combined refractive power made positive. With these,the entire lens system takes the retrofocus type.

[0069] For the telephoto end, the second and third lens units arepositioned so closely that their combined refractive power becomesnegative. The fourth and fifth lens units and also the sixth lens unitare positioned close to each other so that their combined refractivepower becomes negative or weakly positive. Further, the stop ispositioned near the third lens unit.

[0070] As the configuration of the lens units is made to vary in such away, it is in the wide-angle end that, although the refractive powerarrangement is made nearly of the retrofocus type, the rearmost or sixthlens unit is permitted to be a negative lens unit, thereby wellcorrecting asymmetric aberrations such as coma. With the same lensconfiguration, when in the telephoto end, the refractive powerarrangement becomes the telephoto type. The lens system thus takes acompact form, while still permitting all aberrations to be correctedwell.

[0071] In addition, the refractive power of the fourth lens unit isspecified by the condition (1) to minimize the variation of aberrationswith zooming. The inequalities of condition (1) give a range for theratio of the focal length of the fourth lens unit to the longest focallength of the entire system and have an aim chiefly to define arefractive power arrangement that assures maintenance of good stabilityof aberration correction throughout the zooming range.

[0072] When the lower limit of the condition (1) is exceeded, as thismeans that the absolute value of the focal length of the fourth lensunit is too small as compared with the focal length for the telephotoend of the entire system, it becomes necessary to make relatively largethe absolute value of the focal length of the sixth lens unit. At thistime, particularly in the wide-angle end, the symmetry of the refractivepower arrangement is worsened. So, it becomes difficult to correct comaand other asymmetric aberrations. Conversely when the upper limit of thecondition (1) is exceeded, as this means that the absolute value of thefocal length of the fourth lens unit is too large as compared with thelongest focal length of the entire system, it becomes difficult tocorrect the variation of spherical aberration with zooming, since thiscorrection is done mainly by the fourth lens unit.

[0073] For the zoom lens of the invention, use is made of the six lensunits whose refractive powers are specified in sign as described abovein combination with the variations of the air separations with zoomingfrom the wide-angle end to the telephoto end specified as describedabove. Further, the refractive power arranged is made to satisfy thecondition (1) described above. Thus, all aberrations are corrected well,so that high optical performance is maintained stable over the entirezooming range.

[0074] To further improve the variation of aberrations with zooming, andto obtain a high image quality over the entire area of the image frame,the invention sets forth the following additional conditions:

0.1<|f2/fT|<0.18   (2)

0.12<|f6/fT|<0.3   (3)

[0075] where f2 and f6 are the focal lengths of the second and sixthlens units, respectively.

[0076] The inequalities of condition (2) are concerned with the ratio ofthe focal length of the second lens unit which has the negativerefractive power to the longest focal length of the entire system, andthe inequalities of condition (3) are concerned with the ratio of thefocal length of the sixth lens unit which has the negative refractivepower to the longest focal length of the entire system.

[0077] The conditions (2) and (3) are combined with the condition (1)described before to individually specify the focal lengths of thenegative lens units distributed over the entire system. This combinationrepresents the refractive power arrangement for the zoom lens that canachieve the object of the invention.

[0078] When the lower limit of the condition (2) is exceeded, as thismeans that the absolute value of the second lens unit is too small, itbecomes difficult mainly in the telephoto end to correct coma andastigmatism. Conversely when the upper limit is exceeded, as this meansthat the absolute value of the foal length of the second lens unit istoo large, the zooming movement of the first lens unit must beincreased. So, the physical length of the complete lens increasesobjectionably.

[0079] When the lower limit of the condition (3) is exceeded, as thismeans that the absolute value of the sixth lens unit is too small,distortion of the pincushion type increases mainly in the telephoto end.When the absolute value of the focal length of the sixth lens unit istoo large as exceeding the upper limit, it is in the general case thatthe total length of the complete lens increases objectionably.

[0080] The foregoing has been described in connection with the demeritsresulting from the departure of the focal lengths of the lens units fromthe ranges of the conditions (2) and (3). However, virtually, theabove-described factors are related to one another complicatedly. Afterthe condition (1) is satisfied, when the conditions (2) and (3) aresatisfied, it becomes easy to correct various aberrations well in such amanner that the zoom ratio is kept high enough to 4 or thereabout andthe compact form is maintained.

[0081] In the present invention, at least one of the second and fourthlens units may be made stationary during zooming. If so, regardless ofthe use of the 6-unit type, the structure of the lens barrel can besimplified. (In the numerical examples 1 and 2, the second and fourthlens units remain stationary. In the numerical example 3, the secondlens unit remains stationary.)

[0082] Also, in the present invention, the fourth lens unit isconstructed with a single negative lens of meniscus form convex towardthe image side under the control of the condition (1). By this,variation of mainly spherical aberration with zooming is corrected well.

[0083] Besides these, in the invention, the third lens unit isconstructed with a positive lens and a cemented lens of a positive lensand a negative lens to form two groups with three members. The fifthlens unit is constructed with a cemented lens of a positive lens and anegative lens and a positive lens to form two groups with three members,or with a positive lens and a negative lens to form two groups with twomembers. The sixth lens unit is constructed with a negative lens and acemented lens of a positive lens and a negative lens to form two groupswith three members, or with a cemented lens of a negative lens and apositive lens to form one group with two members, or with a negativelens and a positive lens to form two groups with two members. Withthese, the variation of aberrations with zooming is corrected for a highoptical performance throughout the entire zooming range.

[0084] It should be noted that, as will be described more fully later,the lens system is amenable to the image stabilizing capability bydecentering the second lens unit.

[0085] Next, numerical examples 1 to 3 of the invention are shown. Inthe numerical data for the examples 1 to 3, Ri is the radius ofcurvature of the i-th lens surface, when counted from the object side,Di is the i-th axial lens thickness or air separation, when counted fromthe object side and Ni and νi are respectively the refractive index andAbbe number of the glass of the i-th lens element, when counted from theobject side. The values of the factors in the above-described conditionsfor the numerical examples are listed in Table-1.

NUMERICAL EXAMPLE 1

[0086] Focal Length: 76.51-292.00 Focal Length: 76.51-292.00 F-Number:4.00-5.86 R1 = 103.34 D1 = 2.8 N1 = 1.80518 ν1 = 25.4 R2 = 65.53 D2 =6.6 N2 = 1.51633 ν2 = 64.2 R3 = 1941.34 D3 = 0.2 R4 = 212.98 D4 = 4.2 N3= 1.48749 ν3 = 70.2 R5 = −305.81 D5 = Variable R6 = −115.87 D6 = 1.5 N4= 1.77250 ν4 = 49.6 R7 = 131.18 D7 = 2.8 R8 = −57.65 D8 = 1.5 N5 =1.60311 ν5 = 60.7 R9 = 60.38 D9 = 3.4 N6 = 1.84666 ν6 = 23.8 R10 =313.25 D10 = Variable R11 = 366.28 D11 = 3.4 N7 = 1.48749 ν7 = 70.2 R12= −89.07 D12 = 0.2 R13 = 50.08 D13 = 5.2 N8 = 1.60311 ν8 = 60.7 R14 =−90.47 D14 = 1.5 N9 = 1.33400 ν9 = 37.2 R15 = −5450.60 D15 = 2.0 R16 =(Stop) D16 = Variable R17 = −85.14 D17 = 2.5 N10 = 1.51633 ν10 = 64.2R18 = −114.60 D18 = Variable R19 = 124.60 D19 = 4.4 N11 = 1.60311 ν11 =60.7 R20 = −38.67 D20 = 1.5 N12 = 1.80518 ν12 = 25.4 R21 = −181.93 D21 =0.2 R22 = 56.62 D22 = 3.4 N13 = 1.51633 ν13 = 64.2 R23 = −206.31 D23 =Variable R24 = −51.93 D24 = 1.5 N14 = 1.77250 ν14 = 49.6 R25 = 71.28 D25= 1.4 R26 = 641.53 D26 = 4.0 N15 = 1.80518 ν15 = 25.4 R27 = −38.69 D27 =1.5 N16 = 1.69680 ν16 = 55.5 R28 = −907.33 Variable Focal LengthSeparations 76.51 135.00 292.00 D5 4.00 28.11 59.00 D10 36.01 21.37 2.49D16 3.00 17.63 36.52 D18 30.24 16.59 15.51 D23 16.09 12.99 2.99

NUMERICAL EXAMPLE 2

[0087] Focal Length: 76.53-291.99 F-Number: 4.05-5.78 R1 = 117.46 D1 =2.8 N1 = 1.80518 ν1 = 25.4 R2 = 70.46 D2 = 6.1 N2 = 1.51633 ν2 = 64.2 R3= 896.98 D3 = 0.2 R4 = 110.38 D4 = 5.4 N3 = 1.48749 ν3 = 70.2 R5 =−444.29 D5 = Variable R6 = −103.08 D6 = 1.5 N4 = 1.77250 ν4 = 49.6 R7 =79.32 D7 = 2.8 R8 = 70.54 D8 = 1.5 N5 = 1.60311 ν5 = 60.7 R9 = 43.52 D9= 3.6 N6 = 1.84666 ν6 = 23.8 R10 = 188.82 D10 = Variable R11 = −70.72D11 = 4.1 N7 = 1.60311 ν7 = 60.7 R12 = −95.89 D12 = 0.2 R13 = 69.47 D13= 4.6 N8 = 1.60311 ν8 = 60.7 R14 = −58.59 D14 = 1.5 N9 = 1.83400 ν9 =37.2 R15 = 275.47 D15 = 2.0 R16 = (Stop) D16 = Variable R17 = −56.86 D17= 2.5 N10 = 1.51633 ν10 = 64.2 R18 = −84.28 D18 = Variable R19 = 137.95D19 = 5.4 N11 = 1.60311 ν11 = 60.7 R20 = −33.51 D20 = 1.5 N12 = 1.76182ν12 = 26.5 R21 = −91.67 D21 = 0.2 R22 = 66.61 D22 = 3.3 N13 = 1.60311ν13 = 60.7 R23 = −2072.51 D23 = Variable R24 = −67.27 D24 = 1.5 N14 =1.77250 ν14 = 49.6 R25 = 29.73 D25 = 4.0 N15 = 1.80518 ν15 = 25.4 R26 =92.37 Variable Focal Length Separations 76.53 126.57 291.99 D5 4.0028.75 59.00 D10 26.33 18.10 2.56 D16 4.00 12.23 27.77 D18 35.64 28.1227.11 D23 20.82 16.71 3.47

NUMERICAL EXAMPLE 3

[0088] Focal Length: 75.99-291.99 F-Number: 4.05-5.75 R1 = 94.35 D1 =2.8 N1 = 1.80518 ν1 = 25.4 R2 = 61.27 D2 = 7.3 N2 = 1.51633 ν2 = 64.2 R3= −757.11 D3 = 0.2 R4 = 313.60 D4 = 3.6 N3 = 1.48749 ν3 = 70.2 R5 =−481.24 D5 = Variable R6 = −114.27 D6 = 1.5 N4 = 1.77250 ν4 = 49.6 R7 =146.02 D7 = 2.5 R8 = −71.58 D8 = 1.5 N5 = 1.60311 ν5 = 60.7 R9 = 41.03D9 = 3.3 N6 = 1.84666 ν6 = 23.8 R10 = 109.42 D10 = Variable R11 = 127.60D11 = 3.6 N7 = 1.48749 ν7 = 70.2 R12 = −84.87 D12 = 0.2 R13 = 42.12 D13= 5.3 N8 = 1.51633 ν8 = 64.2 R14 = −76.46 D14 = 1.5 N9 = 1.83400 ν9 =37.2 R15 = 1363.46 D15 = 2.0 R16 = (Stop) D16 = Variable R17 = −65.36D17 = 2.5 N10 = 1.51633 ν10 = 64.2 R18 = −78.94 D18 = Variable R19 =76.31 D19 = 4.1 N11 = 1.69680 ν11 = 55.5 R20 = −43.97 D20 = 1.7 R21 =−38.11 D21 = 1.5 N12 = 1.84666 ν12 = 23.8 R22 = −111.62 D22 = VariableR23 = −58.91 D23 = 1.5 N13 = 1.77250 ν13 = 49.6 R24 = 35.27 D24 = 3.0R25 = 44.47 D25 = 3.7 N14 = 1.74077 ν14 = 27.8 R26 = −473.11 VariableFocal Length Separations 75.99 135.00 291.99 D5 4.00 29.99 59.00 D1038.88 24.09 2.48 D16 4.00 12.96 28.08 D18 20.43 13.00 13.16 D22 19.0515.18 2.99

[0089] TABLE 1 Condition Numerical Example No. Factor 1 2 3 (1) |f4/fT|2.262 1.197 2.689 (2) |f2/fT| 0.155 0.135 0.149 (3) |f6/fT| 0.166 0.1770.231

[0090] According to the invention, as described above, the zoom lens isconstructed with six lens units of specified refractive powers in total,wherein proper rules are set forth for the refractive powers of the lensunits and for the relation in which the lens units move when zooming, sothat the number of constituent lenses is reduced to a minimum to insurethat a shortening of the total length of the entire lens system isachieved, while still permitting high optical performance to bemaintained throughout the entire zooming range. Thus, a zoom lens of thetelephoto type having a range of about 4 is achieved.

[0091] Another embodiment in which further improvements are made isdescribed below.

[0092] Numerical examples 4 to 7 of zoom lenses of the invention areshown in FIGS. 7(A), 7(B) and 7(B) through FIGS. 10(A), 10(B) and 10(C).The aberrations of the zoom lenses of the numerical examples 4 to 7 areshown in FIGS. 11(A), 11(B) and 11(C) through FIGS. 14(A), 14(B) and14(C), with suffix (A) in the wide-angle end, suffix (B) in a middleposition and suffix (C) in the telephoto end.

[0093] The zoom lens comprises, from front to rear, a first lens unit L1of positive refractive power, a second lens unit L2 of negativerefractive power, a third lens unit L3 of positive refractive power, afourth lens unit L4 of negative refractive power, a fifth lens unit L5of positive refractive power and a sixth lens unit L6 of negativerefractive power. SP stands for a stop. The arrows indicate the loci ofmotion of the lens units when zooming from the wide-angle end to thetelephoto end.

[0094] One of the characteristic features of the present embodiment isthat, for zooming purposes, certain ones of the lens units are made tomove in such relation as illustrated.

[0095] In more detail, when zooming from the wide-angle end to thetelephoto end, the separation between the first and second lens unitsincreases, the separation between the second and third lens unitsdecreases, the separation between the third and fourth lens unitsincreases, the separation between the fourth and fifth lens unitincreases and the separation between the fifth and sixth lens unitsdecreases.

[0096] Along with this, an additional condition is set forth as follows:

0.3<ln Z ₂ /ln Z<1  (4)

[0097] where ln represents natural logarithm wherein Z₂ is the zoomratio of the second lens unit and Z is the zoom ratio of the entiresystem.

[0098] When these features or conditions are satisfied, a proper effectof varying the focal length is produced, thereby making it easier toextend the zooming range, while still permitting a shortening of thetotal length of the entire system to be achieved. The stop SP is madeaxially movable in unison with the third lens unit.

[0099] It is to be noted that, for the numerical examples 4, 5 and 6,the second and fourth lens units remain stationary during zooming. Forthe numerical example 7, the second, fourth and sixth lens units remainstationary during zooming.

[0100] In the zoom lens of the invention, for the wide-angle end, thefirst and second lens units are positioned so closely that theircombined refractive power becomes negative. The third and fourth lensunits and also the fifth lens unit are positioned close to each other.In addition, the third and those that follow have their overallrefractive power made negative. With these, the lens system takes as awhole the retrofocus type.

[0101] For the telephoto end, the first and second lens units are spacedapart largely. The second and third lens units are positioned so closelythat their combined refractive power becomes negative. The fifth andsixth lens units are positioned so closely that their combinedrefractive power becomes negative or weakly positive. The stop ispositioned adjacent to the third lens unit. With these, the lens systemtakes as a whole the telephoto type.

[0102] In the present invention, by using the lens configuration assuch, the refractive power arrangement is made to be nearly of theretrofocus type in the wide-angle end. Nonetheless, the rearmost orsixth lens unit is permitted to be a negative lens unit, thereby wellcorrecting coma and other asymmetric aberrations. Along with this, it isin the telephoto end that as the refractive power arrangement takes thetelephoto type, compact form is produced and at the same time sphericalaberration and others are corrected well.

[0103] In particular, the separation between the fourth and fifth lensunits is made wider in the telephoto end than in the wide-angle end.This decreases the amount of spherical aberration produced from thefifth lens unit in the telephoto end, thus reducing the contribution ofthe sixth lens unit to the correction of spherical aberration for thetelephoto end.

[0104] Next, an explanation is given to the technical significance ofthe above-described condition (4). The factor in this conditionrepresents how much share the second lens unit should take in varyingthe focal length of the entire system. Mainly in view of well correctingthe variation of all aberrations with zooming, the inequalities ofcondition (4) give a possible rang for the contribution of the secondlens unit to the variation of the focal length. When the lower limit ofthe condition (4) is exceeded, as this means that the second lens unittakes too small a share in varying the focal length, or the zoom ratioof the second lens unit is too small as compared with the zoom ratio ofthe entire system, the contribution of third lens unit and those thatfollow to the variation of the focal length becomes greater. In the caseof laying a large proportion of the zoom ratio on the third lens unitand those that follows, because the total movement of each of these lensunits cannot be taken so much long, such a violation would result instrengthening the refractive power of every one of the lens units. As aresult, all aberrations could be hardly corrected without having toincrease the number of constituent lenses objectionably.

[0105] Conversely when the upper limit of the condition (4) is exceeded,as this means that the second lens unit takes too large a share invarying the focal length, or the zoom ratio of the second lens unit istoo high as compared with the zoom ratio of the entire system, the thirdlens unit and the later has to perform inverse variation of the focallength, thus worsening the efficiency with which to vary the focallength. In order to perform a great variation of the focal length by thesecond lens unit, the movement of the second lens unit has to increaselargely. This is disadvantageous at improving the compact form. Further,as the varied amount of aberrations by the first and second lens unitsincreases, the number of constituent lenses in each lens unit is causedto increase objectionably.

[0106] Incidentally, in the invention, on correction of aberrations, itis further preferable to alter the range for the factor of the condition(4) as follows:

0.5<ln Z ₂ /ln Z<1  (4a)

[0107] The zoom lens of the invention uses six lens units whoserefractive powers are of the signs described above, and zooming isperformed by varying the separations as specified above when zoomingfrom the wide-angle end to the telephoto end. Further, by determiningthe contribution to the variation of the focal length based on thecondition (4). The aberrations are corrected particularly well and highoptical performance is obtained throughout the entire zooming range.

[0108] In the invention, to further reduce the range of variation ofaberrations with zooming and to obtain high optical performancethroughout the entire area of the image frame, it is preferred tosatisfy the following condition:

0.5<f1/{square root}{square root over (fW×fT)}<3.0  (5)

[0109] where f1 is the focal length of the first lens unit, and fW andfT are the shortest and longest focal lengths of the entire system.

[0110] The inequalities of condition (5) are to determine therelationship between the focal length of the first lens unit of positiverefractive power and the focal lengths of the entire system for thewide-angle and telephoto ends. Being combined with the before describedcondition (4), the condition (5) gives a range for the refractive powerof the first lens unit, as is necessary for the second lens unit tocontribute to the variation of the focal length. When the lower limit ofthe condition (5) is exceeded, as this means that the focal length ofthe first lens unit is too small, it becomes difficult to correct comaand astigmatism mainly in the telephoto end. Conversely when the focallength of the first lens unit is too long as exceeding the upper limit,the zooming movement of the first lens unit must be increased largely,causing the total length of the entire system to increase objectionably.

[0111] In the invention, at least one of the second, fourth and sixthlens units is made stationary during zooming. With this, despite the useof the 6-unit type or a relatively large number of lens units, it ismade possible to limit the number of movable lens units for zooming to aminimum.

[0112] In the invention, the fourth lens unit is constructed with asingle lens or a cemented lens of meniscus form convex toward the objectside or image side, thereby well correcting the variation of mainlyspherical aberration with zooming. The third lens unit is constructedwith a positive lens and cemented lens of a positive lens and a negativelens to form two groups with three members. The fifth lens unit isconstructed with a cemented lens of a negative lens and a positive lensto form one group with two members. The sixth lens unit is constructedwith a cemented lens of a negative lens and a positive lens to form onegroup with two members. With these, the variation of aberrations withzooming is corrected for high optical performance throughout the entirezooming range.

[0113] Next, numerical examples 4 to 7 of the invention are shown. Inthe numerical data for the examples 4 to 7, Ri is the radius ofcurvature of the i-th lens surface, when counted from the object side,Di is the i-th axial thickness or air separation, when counted from theobject side, and Ni and νi are respectively the refractive index andAbbe number of the glass of the i-th lens element, when counted from theobject side.

NUMERICAL EXAMPLE 4

[0114] Focal Length: 76.50-293.52; F-Number: 4.1-5.8 R1 = 88.37 D1 = 2.8N1 = 1.80518 ν1 = 25.4 R2 = 58.63 D2 = 6.8 N2 = 1.51633 ν2 = 64.2 R3 =2198.36 D3 = 0.2 R4 = 184.51 D4 = 4.6 N3 = 1.48749 ν3 = 70.2 R5 =−437.16 D5 = Variable R6 = −109.28 D6 = 1.5 N4 = 1.77250 ν4 = 49.6 R7 =68.67 D7 = 4.5 R8 = −43.04 D8 = 1.5 N5 = 1.51633 ν5 = 64.2 R9 = 71.91 D9= 3.5 N6 = 1.84666 ν6 = 23.8 R10 = −762.51 D10 = Variable R11 = 91.13D11 = 4.3 N7 = 1.60311 ν7 = 60.7 R12 = −79.05 D12 = 0.2 R13 = 55.87 D13= 4.5 N8 = 1.48749 ν8 = 70.2 R14 = −78.29 D14 = 1.5 N9 = 1.83400 ν9 =37.2 R15 = 302.40 D15 = 2.5 R16 = (Stop) D16 = Variable R17 = −37.76 D17= 2.5 N10 = 1.51633 ν10 = 64.2 R18 = −42.46 D18 = Variable R19 = 50.91D19 = 2.0 N11 = 1.80518 ν11 = 25.4 R20 = 30.74 D20 = 6.0 N12 = 1.51633ν12 = 64.2 R21 = −106.16 D21 = Variable R22 = −41.02 D22 = 1.5 N13 =1.77250 ν13 = 49.6 R23 = 73.44 D23 = 3.7 N14 = 1.80518 ν14 = 25.4 R24 =−197.05 Variable Focal Length Separations 76.50 133.51 293.52 D5 4.0031.50 59.00 D10 32.94 21.72 2.50 D16 4.00 15.22 34.44 D18 17.41 11.3534.10 D22 27.83 22.54 3.00

ln Z ₂ /ln Z=0.8975; f1/{square root}{square root over (fW·fT)}=0.8742

NUMERICAL EXAMPLE 5

[0115] Focal Length: 76.52-299.96; F-Number: 4.1-5.8 R1 = 101.86 D1 =2.8 N1 = 1.80518 ν1 = 25.4 R2 = 66.06 D2 = 6.8 N2 = 1.51633 ν2 = 64.2 R3= −2991.10 D3 = 0.2 R4 = 160.98 D4 = 4.6 N3 = 1.48749 ν3 = 70.2 R5 =−491.58 D5 = Variable R6 = −141.58 D6 = 1.5 N4 = 1.77250 ν4 = 49.6 R7 =63.57 D7 = 4.5 R8 = 45.92 D8 = 1.5 N5 = 1.51633 ν5 = 64.2 R9 = 55.41 D9= 3.5 N6 = 1.84666 ν6 = 23.8 R10 = 549.96 D10 = Variable R11 = 101.98D11 = 4.3 N7 = 1.60311 ν7 = 60.7 R12 = −97.26 D12 = 0.2 R13 = 60.55 D13= 4.5 N8 = 1.48749 ν8 = 70.2 R14 = −58.42 D14 = 1.5 N9 = 1.83400 ν9 =37.2 R15 = 2309.85 D15 = 2.5 R16 = (Stop) D16 = Variable R17 = 62.59 D17= 4.0 N10 = 1.51633 ν10 = 64.2 R18 = 46.98 D18 = Variable R19 = 75.37D19 = 2.0 N11 = 1.80518 ν11 = 25.4 R20 = 47.71 D20 = 6.0 N12 = 1.51112ν12 = 60.5 R21 = −107.42 D21 = Variable R22 = −43.25 D22 = 1.5 N13 =1.77250 ν13 = 49.6 R23 = −137.02 D23 = 3.7 N14 = 1.80518 ν14 = 25.4 R24= −69.56 Variable Focal Length Separations 76.52 156.31 299.96 D5 4.0031.50 59.00 D10 41.16 22.48 3.90 D16 4.00 22.68 41.26 D18 17.90 −3.1820.03 D22 45.25 31.82 8.27

ln Z ₂ /ln Z=0.8799; f1/{square root}{square root over (fW·fT)}=0.8644

NUMERICAL EXAMPLE 6

[0116] Focal Length: 77.37-291.70; F-Number: 4.1-5.8 R1 = 72.66 D1 = 2.8N1 = 1.80518 ν1 = 25.4 R2 = 47.75 D2 = 9.0 N2 = 1.51633 ν2 = 64.2 R3 =−421.68 D3 = 0.2 R4 = 189.95 D4 = 4.6 N3 = 1.48749 ν3 = 70.2 R5 = 439.01D5 = Variable R6 = −94.89 D6 = 1.5 N4 = 1.77250 ν4 = 49.6 R7 = 51.91 D7= 4.5 R8 = −73.79 D8 = 1.5 N5 = 1.51633 ν5 = 64.2 R9 = 54.29 D9 = 3.5 N6= 1.84666 ν6 = 23.8 R10 = 535.37 D10 = Variable R11 = 55.67 D11 = 6.5 N7= 1.60311 ν7 = 60.7 R12 = −57.70 D12 = 0.2 R13 = 54.57 D13 = 6.2 N8 =1.48749 ν8 = 70.2 R14 = −46.16 D14 = 1.5 N9 = 1.83400 ν9 = 37.2 R15 =589.80 D15 = 2.5 R16 = (Stop) D16 = Variable R17 = −37.95 D17 = 2.0 N10= 1.80518 ν10 = 25.4 R18 = −29.85 D18 = 2.0 N11 = 1.51633 ν11 = 64.2 R19= −404.46 D19 = Variable R20 = 55.41 D20 = 2.0 N12 = 1.80518 ν12 = 25.4R21 = 26.63 D21 = 6.0 N13 = 1.51633 ν13 = 64.2 R22 = −48.33 D22 =Variable R23 = −36.80 D23 = 1.5 N14 = 1.77250 ν14 = 49.6 R24 = 66.11 D24= 3.7 N15 = 1.80518 ν15 = 25.4 R25 = −179.29 Variable Focal LengthSeparations 77.37 114.23 291.70 D5 4.00 24.00 44.00 D10 33.17 26.84 0.60D16 2.01 8.33 34.58 D19 10.91 12.19 14.95 D23 27.29 20.54 2.18

ln Z ₂ /ln Z=0.5623; f1/{square root}{square root over (fW·fT)}=0.8626

NUMERICAL EXAMPLE 7

[0117] Focal Length: 76.60-291.94; F-Number: 4.1-5.8 R1 = 105.68 D1 =2.8 N1 = 1.80518 ν1 = 25.4 R2 = 66.24 D2 = 6.8 N2 = 1.51633 ν2 = 64.2 R3= −729.65 D3 = 0.2 R4 = 207.49 D4 = 4.6 N3 = 1.48749 ν3 = 70.2 R5 =−314.15 D5 = Variable R6 = −98.99 D6 = 1.5 N4 = 1.77250 ν4 = 49.6 R7 =71.80 D7 = 4.5 R8 = 33.15 D8 = 1.5 N5 = 1.51633 ν5 = 64.2 R9 = 81.89 D9= 3.5 N6 = 1.84666 ν6 = 23.8 R10 = −162.12 D10 = Variable R11 = 72.84D11 = 4.3 N7 = 1.60311 ν7 = 60.7 R12 = 67.18 D12 = 0.2 R13 = 56.13 D13 =4.5 N8 = 1.48749 ν8 = 70.2 R14 = 56.03 D14 = 1.5 N9 = 1.83400 ν9 = 37.2R15 = 146.88 D15 = 2.5 R16 = (Stop) D16 = Variable R17 = −36.43 D17 =2.5 N10 = 1.51633 ν10 = 64.2 R18 = −43.73 D18 = Variable R19 = 45.08 D19= 2.0 N11 = 1.80518 ν11 = 25.4 R20 = 31.75 D20 = 7.0 N12 = 1.51112 ν12 =60.5 R21 = −111.22 D21 = Variable R22 = −41.36 D22 = 1.5 N13 = 1.77250ν13 = 49.6 R23 = 193.42 D23 = 3.7 N14 = 1.80518 ν14 = 25.4 R24 = −149.01Variable Focal Length Separations 76.60 119.14 291.94 D5 4.00 31.5059.00 D10 35.27 27.29 2.12 D16 25.05 33.04 58.20 D18 5.62 8.76 25.13 D2124.30 21.17 4.79

ln Z ₂ /ln Z=0.9199; f1/{square root}{square root over (fW·fT)}=0.8614

[0118] According to the invention, as described above, the zoom lens isconstructed with six lens units of specified refractive powerarrangement, and proper rules are set forth for the refractive powers ofthe lens units and for the relation in which the lens groups move toeffect zooming. With these, the number of constituent lenses is reducedand the total length of the entire system is shortened, while stillpermitting high optical performance to be maintained throughout theentire zooming range. Thus, a zoom lens of the telephoto type having arange of about 4 with improvements of the image quality and compact formis achieved.

[0119] Next, the above-described zoom lens is improved in order toinsure that part of this zoom lens can be decentered to stabilize theimage. Such a zoom lens is described below.

[0120]FIG. 15 is a diagram of geometry to explain the variation ofparaxial refractive power arrangement and FIGS. 16(A), 16(B) and 16(C)are longitudinal section view of a numerical example 8 of a zoom lensemploying the form of FIG. 15. FIG. 17 and FIGS. 18(A), 18(B) and 18(C)are a diagram of geometry and longitudinal section views of a numericalexample 9 of a zoom lens. In FIG. 15 and FIG. 17, the upper halfrepresents the wide-angle side, and the lower half the telephoto side.The arrows indicate the loci of the lens units when zooming from thewide-angle end to the telephoto end. Of the lens block diagrams, FIGS.16(A) and 18(A) are in the wide-angle end, FIGS. 16(B) and 18(B) are ina middle position and FIGS. 16(C) and 18(C) in the telephoto end.

[0121] In the numerical example 8 of FIG. 15 and FIGS. 16(A), 16(B) and16(C), the zoom lens comprises, from front to rear, a first lens unit L1of positive refractive power, a second lens unit L2 of negativerefractive power, a third lens unit L3 of positive refractive power, afourth lens unit L4 of positive refractive power and a fifth lens unitL5 of negative refractive power. SP stands for a stop and IP for animage plane. When zooming from the wide-angle end to the telephoto end,the second lens unit remains stationary, while the first, third, fourthand fifth lens units move axially in differential relation as indicatedby the arrows. The second lens unit is used as a decentering lens unitarranged on vibrations of the optical system to move in directionsperpendicular to an optical axis to correct the shaking of an image.

[0122] In the numerical example 9 of FIG. 17 and FIGS. 18(A), 18(B) and18(C), the zoom lens comprises, from front to rear, a first lens unit L1of positive refractive power, a second lens unit L2 of negativerefractive power, a third lens unit L3 of positive refractive power, afourth lens unit L4 of negative refractive power, a fifth lens unit L5of positive refractive power and a sixth lens unit L6 of negativerefractive power. SP stands for a stop and IP for an image plane. Whenzooming from the wide-angle end to the telephoto end, the second andfourth lens units remain stationary, while the first, third, fifth andsixth lens units move axially in differential relation as indicated bythe arrows. The second lens unit is used as a decentering lens unitarranged on vibrations of the optical system to move in directionsperpendicular to an optical axis to correct the shaking of an image.

[0123] As is understandable from the foregoing, the invention uses atleast three lens units in constructing a zoom lens. Of these, at leasttwo are made to move along a common optical axis to effect zooming. Inthe space between the two movable lens units for zooming there ispositioned a lens unit stationary during zooming. This lens unit is madeto move to directions perpendicular to the optical axis in such a waythat when the optical system vibrates, the shaking of an image iscorrected.

[0124] In particular, in the invention, a zoom lens comprises, fromfront to rear, a first lens unit having a positive refractive power andaxially movable for zooming, a second lens unit having a negativerefractive power and stationary during zooming, and a rear lens unitcomprised of at least one lens sub-unit, or a plurality of lenssub-units, axially movable for zooming and whose overall refractivepower is positive, wherein the second lens unit is made to move indirections perpendicular to the optical axis to correct the shaking ofan image when the optical system vibrates.

[0125] With the features described above, the invention is to correctthe shaking of the image with respect to a shooting line, and at thesame time to minimize the decentering aberrations the second lens unitproduces when moved (decentered) in the directions perpendicular to theoptical axis, thus maintaining good optical performance.

[0126] In the numerical example 8 of FIG. 15 and FIGS. 16(A), 16(B) and16(C), letting the separation between the i-th and (i+1)st lens unitsfor the wide-angle end and the telephoto end be denoted by DiW and DiT,respectively, when zooming from the wide-angle end to the telephoto end,the selected ones of the lens units are moved in such relation as tosatisfy the following conditions:

D1W<D1T

D2W>D2T

D4W>D4T

[0127] In the numerical example 8, during zooming, the lens units aremoved so as to satisfy the above-described conditions, thereby obtaininga zoom lens of high zoom ratio with minimization of the entire lenssystem. It is to be noted that, in the present embodiment, the secondlens unit may otherwise be made axially movable for zooming. Accordingto this, it becomes easier to extend the zooming range, and thevariation of aberrations with zooming can be corrected well.

[0128] In the numerical example 9 of FIG. 17 and FIGS. 18(A), 18(B) and18(C), letting the separation between the i-th and (i+1)st lens unitsfor the wide angle end and the telephoto end be denoted by DiW and DiT,respectively, when zooming from the wide-angle end to the telephoto end,the selected ones of the lens units are moved in such relation as tosatisfy the following conditions:

D1W<D1T

D2W>D2T

D3W<D3T

D5W>D5T

[0129] In the numerical examples 9, during zooming, the lens units aremoved in such relation as to satisfy the conditions described above,thereby minimizing the size of the entire lens system, so that a zoomlens of high range is obtained. It is to be noted that in the presentembodiment, the second lens unit may otherwise be made axially movablefor zooming. According to this, it becomes easier to extend the zoomingrange. Also, the variation of aberrations with zooming can be correctedwell.

[0130] In the numerical examples 8 and 9, it is preferred to set forthadditional conditions in order to fulfill the requirements of minimizingthe bulk and size of the entire lens system and of reducing thedecentering aberrations when the shaking of an image is corrected forgood stability of optical performance.

[0131] (i) The focal length fa of the aforesaid decentering lens unitlies in a range given by the following condition:

0.15<|fa/{square root}{square root over (fW·fT)}|<0.5  (6)

[0132] where fw and fT are the shortest and longest focal lengths of theentire system, respectively.

[0133] The inequalities of condition (6) give a range for the ratio ofthe focal length of the decentering lens unit (second lens unit) to theshortest and longest focal lengths of the zoom lens. When the lowerlimit of the condition (6) is exceeded, as this means that the focallength of the decentering lens unit is too short, it becomes difficultto well correct the variation of aberrations with zooming. So, the zoomratio cannot be much extended as desired. Another problem is that a fewlens elements do not suffice for making up the decentering lens unit.So, it is not suited to improve the compact form.

[0134] Conversely when the upper limit of condition (6) is exceeded, asthis means the focal length of the decentering lens unit is too long, itis advantageous at correcting various aberrations, but the sensitivityof the decentering lens to decentering (the ratio of the deviation ofthe decentering lens unit to the deviation of the image with respect tothe line of sight) becomes impossible to increase. For this reason, themovement of the decentering lens unit for correcting the shaking must beincreased. Moreover, the zooming movement of each lens unit increaseslargely. This is contradictory to improvement of the compact form.

[0135] (ii) Letting the overall focal lengths for the wide-angle andtelephoto ends of those lens units which are positioned on the objectside of the decentering lens unit be denoted by foW and foT,respectively, and the overall focal lengths for the wide-angle andtelephoto ends of the decentering lens unit and those lens units whichlie on the object side of the decentering lens unit by frW and frT,respectively, the following conditions are satisfied:

0.20<|foW/frW|<1.50  (7)

0.80<|foT/frT|<6.0  (8)

[0136] The inequalities of condition (7) give a range for the ratio ofthe overall focal length for the wide-angle end of those lens unitswhich are positioned ahead of the decentering lens unit that moves inthe directions perpendicular to the optical axis when stabilizing animage to the overall focal length of the decentering lens unit and thosethat are positioned on the object side of the decentering lens unit. Theinequalities of condition (8) give a range for the same except for thetelephoto end.

[0137] The factors in the conditions (7) and (8) virtually represent theratio of the reduced angles of inclination of the axial light ray in theparaxial zone before and after the decentering lens unit that moves inthe directions perpendicular to the optical axis when correcting theshaking. When the refractive power arrangement satisfies theseconditions, good correction of decentering aberrations results.Therefore, when the values of the factors fall outside the rangesdefined by the conditions (7) and (8), problems arise in that a simplelens construction can no longer correct decentering aberrations well andthat the decentering sensitivity can no longer be increasedsufficiently.

[0138] It is to be noted in connection with the conditions (7) and (8)that the reason why the condition (7) is wider in the numerical rangethan the condition (8) is that the displacement of the image for anequivalent angle of vibration is smaller when in the wide-angle end thanin the telephoto end and, therefore, the amount of decenteringaberrations produced, too, becomes lesser.

[0139] Next, the optical features of the zoom lens having the imagestabilizing function of the invention are described below.

[0140] In general, if part of the optical system or one lens unit isparallel decentered to correct the shaking of an image, the imagequality is caused to lower by the decentering aberrations produced. Nowassuming that in any refractive power arrangement, a lens unit is mademovable in directions perpendicular to the optical axis for the purposeof correcting the shaking of an image, an explanation will be made aboutthe production of decentering aberrations from the standpoint of theaberration theory on the basis of the method revealed by Yoshiya Matsuiat the 23rd lecture meeting on applied physics in Japan (1962).

[0141] When part of the zoom lens, say lens unit P, is paralleldecentered by E, the amount of aberrations ΔY1 the entire systemproduces is expressed by an equation (a) of the sum of the amount ofaberrations ΔY that occurs before the decentering and the amount ofdecentering aberrations ΔY(E) produced by the decentering. Here, theamount of aberrations ΔY is expressed by spherical aberration (I), coma(II), astigmatism (III), Petzval sum (P) and distortion (Y). The amountof decentering aberrations ΔY(E) is expressed by an equation (c) ofprimary decentering coma (IIE), primary decentering astigmatism (IIIE),primary decentering curvature of field (PE), primary decenteringdistortion (VE1), primary decentering distortion added aberration (VE2),and primary original point movement (ΔE).

[0142] Equations (d) to (i) for the aberrations (ΔE) to (VE2) areexpressed under the condition that for the zoom lens having the lensunit P made to parallel decenter, the on-axial and off-axial light raysare incident on the lens unit P at an angle α_(p), αa_(p), by using theaberration coefficients I_(p), II_(p), III_(p), P_(p) and V_(p) of thelens unit P and also, as those lens units which are positioned on theimage side of the lens unit P are all taken as one q-th lens unit, byusing its aberration coefficients I_(q), II_(q), III_(q), P_(q) andV_(q).

ΔY1=ΔY+ΔY(E)  (a)

[0143] $\begin{matrix}\begin{matrix}{{\Delta \quad Y} = \quad {{- \left( {1/\left( {2\alpha_{K}^{\prime}} \right)} \right)}\left( {{\left( {N_{1}{\tan \quad}_{\omega}} \right)^{3}\cos \quad {\varphi_{\omega} \cdot V}} +} \right.}} \\{\quad {\left( {N_{1}\tan_{\omega}} \right)^{2}R\left( {{2\cos \quad \varphi_{\omega}{{\cos \left( {\varphi_{R} - \varphi_{\omega}} \right)} \cdot {III}}} +} \right.}} \\{{\quad \left. {\cos \quad {\varphi_{R}\left( {{III} + P} \right)}} \right)} + {\left( {N_{1}\tan_{\omega}} \right)R^{2}\left( {{2\cos \quad \varphi_{R}{\cos \left( {\varphi_{R} - \varphi_{\omega}} \right)}} +} \right.}} \\\left. {{{\quad \left. {\cos \quad \varphi_{\omega}} \right)} \cdot {II}} + {R^{3}\cos \quad {\varphi \cdot I}}} \right)\end{matrix} & (b) \\\begin{matrix}{{\Delta \quad {Y(E)}} = \quad {{- \left( {E/\left( {2\quad \alpha_{K}^{\prime}} \right)} \right)}\left( {{\left( {N_{1}\tan_{\omega}} \right)^{2}\left( {{\left( {2 + {\cos \quad 2\quad \varphi_{\omega}}} \right)\left( {{VE}\quad 1} \right)} - \left( {{VE}\quad 2} \right)} \right)} +} \right.}} \\{\quad {2\left( {N_{1}\tan_{\omega}} \right){R\left( \left( {{2{\cos \left( {\varphi_{R} - \varphi_{\omega}} \right)}} +} \right. \right.}}} \\{\left. {{{\quad \left. {\cos \left( {\varphi_{R} + \varphi_{\omega}} \right)} \right)}({IIIE})} + {\cos \quad \varphi_{R}\cos \quad {\varphi_{\omega} \cdot ({PE})}}} \right) +} \\{{\quad \left. {{R^{2}\left( {2 + {\cos \quad 2\varphi_{R}}} \right)}({IIE})} \right)} - {\left( {E/\left( {2\alpha_{K}^{\prime}} \right)} \right)\left( {\Delta \quad E} \right)}}\end{matrix} & (c) \\{\left( {\Delta \quad E} \right) = \quad {{{- 2}\left( {\alpha_{p}^{\prime} - \alpha_{p}} \right)} = {{- 2}h_{p}\varphi_{p}}}} & (d) \\\begin{matrix}{({IIE}) = \quad {{\alpha \quad a_{p}{II}_{q}} - {\alpha_{p}\left( {{II}_{p} + {II}_{q}} \right)} - {\alpha \quad a_{p}^{\prime}I_{q}} + {\alpha \quad {a_{p}\left( {I_{p} + I_{q}} \right)}}}} \\{= \quad {{h_{p}\varphi_{p}{II}_{q}} - {\alpha_{p}{II}_{p}} - \left( {{{ha}_{p}\varphi_{p}I_{q}} - {\alpha \quad a_{p}I_{p}}} \right)}}\end{matrix} & (e) \\\begin{matrix}{({IIIE}) = \quad {{\alpha_{p}^{\prime}{III}_{q}} - {\alpha_{p}\left( {{III}_{p} + {III}_{q}} \right)} - {\alpha \quad a_{p}^{\prime}I_{q}} + {\alpha \quad {a_{p}\left( {{II}_{p} + {II}_{q}} \right)}}}} \\{= \quad {{h_{p}\varphi_{p}{III}_{q}} - {\alpha_{p}{III}_{p}} - \left( {{{ha}_{p}\varphi_{p}{II}_{q}} - {\alpha \quad a_{p}{II}_{p}}} \right)}}\end{matrix} & (f) \\\begin{matrix}{({PE}) = {{\alpha_{p}^{\prime}P_{q}} - {\alpha_{p}\left( {P_{p} + P_{q}} \right)}}} \\{= {{h_{p}\varphi_{p}P_{q}} - {\alpha_{p}P_{p}}}}\end{matrix} & (g) \\\begin{matrix}{\left( {{VE}\quad 1} \right) = \quad {{\alpha_{p}^{\prime}V_{q}} - {\alpha_{p}\left( {V_{p} + V_{q}} \right)} - {\alpha \quad a_{p}^{\prime}{III}_{q}} + {\alpha \quad {a_{p}\left( {{III}_{p} + {III}_{q}} \right)}}}} \\{= \quad {{h_{p}\varphi_{p}V_{q}} - {\alpha_{p}V_{p}} - \left( {{{ha}_{p}\varphi_{p}{III}_{q}} - {\alpha \quad a_{p}{III}_{p}}} \right)}}\end{matrix} & (h) \\\begin{matrix}{\left( {{VE}\quad 2} \right) = \quad {{\alpha \quad a_{p}P_{q}} - {\alpha \quad {a_{p}\left( {P_{p} + P_{q}} \right)}}}} \\{= \quad {{{ha}_{p}\varphi_{p}P_{q}} - {\alpha \quad a_{p}P_{p}}}}\end{matrix} & (i)\end{matrix}$

[0144] From the equations described above, to minimize the decenteringaberrations produced, it is necessary to make small the values of allthe aberration coefficients I_(p), II_(p), III_(p), P_(p) and V_(p) ofthe lens unit P, or to determine them in good balance so that theaberration coefficients cancel each other out as shown by the equations(a) to (i).

[0145] Next, the optical action of the zoom lens having the imagestabilizing function of the invention is described by taking a model onthe assumption that the photographic optical system shown in FIG. 25 ismoved in part in a direction perpendicular to the optical axis to effectdecentering, when the shaking of the image is corrected.

[0146] First, to realize a sufficiently large correction by asufficiently small decentering movement, it is necessary to makesufficiently large the primary original point movement (ΔE) describedabove with this in mind, a condition is considered for correcting theprimary decentering field curvature (PE). FIG. 25 shows a photographicoptical system comprising, from front to rear, an o-th lens unit, a p-thlens unit and a q-th lens unit, totaling three lens units. Of these, thep-th lens unit is parallel moved in the direction perpendicular to theoptical axis to correct the shaking of the image.

[0147] Here, the refractive powers of the o-th, p-th and q-th lens unitsare denoted by ø_(o), ø_(p) and ø_(q), respectively, the angles ofincidence of the paraxial on-axial and off-axial light rays on any ofthese lens units by α and αa, the heights of incidence of the paraxialon-axial and off-axial light rays by h and ha. The aberrationcoefficients, too, are expressed by using similar suffixes. It is alsoassumed that the lens units each are constructed with a small number oflens elements, and that each of the aberration coefficients tends to beunder-corrected individually.

[0148] Under such a premise, on looking at the Petzval sum of each ofthe lens units, the Petzval sums P_(o), P_(p) and P_(q) of the lensunits are proportional to the refractive powers ø_(o), ø_(p) and ø_(q)of the lens units, approximately satisfying the following relationships:

P _(o) =Cø _(o)

P _(p) =Cø _(p)

P _(q) =Cø _(q) (where C is a constant)  (1)

[0149] Therefore, the primary decentering field curvature (PE) that isproduced when the p-th lens unit is parallel decentered, can berearranged by inserting the equations described above as follows:

(PE)=Cø _(p)(h _(p)ø_(q)−α_(p))  (m)

[0150] To correct the decentering field curvature (PE), therefore,either ø_(p)=0 or ø_(q)=α_(p)/h_(p) must be put. If ø_(p)=0 is used, theoriginal point movement (ΔE) of first degree becomes “0” and correctionof the shaking becomes impossible to perform. So, a solution to satisfyø_(q)=α_(p)/h_(p) has to be sought for. Because h_(p)>0, it is at leastnecessary to make α_(p) and ø_(q) of the same sign.

[0151] (i) For α_(p)>0

[0152] To correct the decentering field curvature, ø_(q)>0 results.Again, inevitably ø_(o)>0 results. Further, at this time, if ø_(p)>0,0<α_(p)<α′_(p)<1. Hence, the primary original point movement (ΔE) isgiven by the following expression:

(ΔE)=−2(α_(p)′−α_(p))>−2  (n)

[0153] That is, the decenter sensitivity (the ratio of the deviation ofthe image to the unity of deviation of the decentering lens unit)becomes smaller than “1”. If ø_(p)=0, as described before, the decentersensitivity is “0”. Therefore, in such a case, it is necessary to haveø_(p)<0.

[0154] (ii) For α_(p)<0

[0155] To correct the decentering field curvature (PE), ø_(q)<0 results.Again, inevitably ø_(o)<0 results. Therefore, further inevitably,ø_(p)>0 results.

[0156] From the above, to make sufficiently large the primary originalpoint movement (ΔE) and make it possible to correct the primarydecentering field curvature (PE), the optical system must take one ofthe following refractive power arrangements: Lens Unit: o p q PowerArrangement a: plus minus plus b: minus plus minus

[0157] These refractive power arrangements are illustrated in FIGS.26(A) and 26(B) respectively.

[0158] In the invention, using such a refractive power arrangement, thezoom lens is constructed. In general, for the zoom lens, proper rulesfor the refractive powers of all the lens units are set forth in orderthat a sufficiently large effect of varying the focal length is realizedwith the entire system in the compact form and at the same time allaberrations are corrected well. To this purpose, it is better that thoselens units which contribute to the variation of the focal length haverelatively strong refractive powers. Also to well correct the variationof aberrations with zooming, it is better that those lens units whichhave their residual aberrations minimized within themselves are selectedto be movable for zooming.

[0159] Which one of the lens units of the zoom lens should be selectedto parallel decenter in directions perpendicular to the optical axiswhen the shaking of an image is corrected is an important problem. Toform such a zoom lens, from the standpoints of providing the possibilityof sufficiently increasing the decenter sensitivity and of making itrelatively easy to correct decentering aberrations, there is a methodthat one of the movable lens units for zooming is applied directly tothe parallel decentering lens unit.

[0160] Meanwhile, for the purpose of improving the compact form of thehousing itself, it is desirable that, as the parallel decentering lensunit, a lens unit of relatively short outer diameter is selected. Toprevent the operating mechanism from becoming complicated, it is alsodesirable to select the fixed lens unit for zooming as the paralleldecentering lens unit.

[0161] In the invention, from the standpoints described above, the zoomlens configuration to be used has the refractive power power arrangementshown in FIG. 26(A) or 26(B), and the o-th and q-th lens units areaxially moved during zooming, while the p-th lens unit remainsstationary.

[0162] In the present invention, not only the movable lens units forzooming are constructed in such a fundamental form, but also the o-thand q-th lens units each may be either in the form of one lens unit, ordivided into a plurality of lens units. According to this, it ispossible to realize a zoom lens which is well corrected for allaberrations. Though each of the foregoing embodiments has been describedas arranging the second lens unit to parallel decenter, it is to beunderstood that, instead of the parallel decentering, it may be rotatedabout a point on the optical axis so that the shaking of the image iscorrected.

[0163] Next, numerical examples 8 and 9 of the invention are shown. Inthe numerical data for the examples 8 and 9, Ri is the radius ofcurvature of the i-th lens surface, when counted from the object side,Di is the i-th axial thickness or air separation, when counted from theobject side, and Ni and νi are respectively the refractive index andAbbe number of the glass of the i-th lens element, when counted from theobject side.

NUMERICAL EXAMPLE 8

[0164] R1 = 101.63 D1 = 2.8 N1 = 1.80518 ν1 = 25.4 R2 = 65.89 D2 = 6.8N2 = 1.51633 ν2 = 64.2 R3 = 1548.89 D3 = 0.2 R4 = 207.11 D4 = 4.2 N3 =1.48749 ν3 = 70.2 R5 = −337.94 D5 = Variable R6 = −125.77 D6 = 1.5 N4 =1.77250 ν4 = 49.6 R7 = 151.03 D7 = 2.8 R8 = −67.50 D8 = 1.5 N5 = 1.61800ν5 = 63.4 R9 = 44.49 D9 = 3.4 N6 = 1.84666 ν6 = 23.8 R10 = 125.21 D10 =Variable R11 = (Stop) D11 = 1.5 R12 = 157.70 D12 = 3.7 N7 = 1.48749 ν7 =70.2 R13 = −86.24 D13 = 0.2 R14 = 46.44 D14 = 5.7 N8 = 1.60311 ν8 = 60.7R15 = −78.17 D15 = 1.5 N9 = 1.83400 ν9 = 37.2 R16 = 308.70 D16 =Variable R17 = 159.74 D17 = 4.6 N10 = 1.60311 ν10 = 60.7 R18 = −35.11D18 = 1.5 N11 = 1.80518 ν11 = 25.4 R19 = −118.95 D19 = 0.2 R20 = 38.80D20 = 4.0 N12 = 1.51633 ν12 = 64.2 R21 = 2284.84 D21 = Variable R22 =−68.32 D22 = 1.5 N13 = 1.77250 ν13 = 49.6 R23 = 34.06 D23 = 3.6 R24 =−162.72 D24 = 1.5 N14 = 1.69680 ν14 = 55.5 R25 = 98.00 D25 = 0.2 R26 =49.20 D26 = 4.3 N15 = 1.80518 ν15 = 25.4 R27 = −185.92 Variable FocalLength Separations 76.72 135.00 291.89 D5 3.50 28.15 58.50 D10 37.0021.31 2.00 D16 40.60 40.85 52.20 D21 9.70 8.40 2.00

NUMERICAL EXAMPLE 9

[0165] R1  =  104.82 D1  = 2.8 N1  = 1.80518 ν1  = 25.4 R2  =  65.22 D2 = 6.6 N2  = 1.51633 ν2  = 64.2 R3  = 1064.41 D3  = 0.2 R4  =  157.35 D4 = 4.6 N3  = 1.51633 ν3  = 64.2 R5  = −339.86 D5  = Variable R6  =−172.44 D6  = 1.5 N4  = 1.77250 ν4  = 49.6 R7  =  63.56 D7  = 4.9 R8  = −34.89 D8  = 1.5 N5  = 1.51633 ν5  = 64.2 R9  =  78.96 D9  = 3.5 N6  =1.84666 ν6  = 23.8 R10 = −270.70 D10 = Variable R11 =  63.23 D11 = 4.4N7  = 1.60311 ν7  = 60.7 R12 =  −77.78 D12 = 0.2 R13 =  57.33 D13 = 4.8N8  = 1.48749 ν8  = 70.2 R14 =  −59.18 D14 = 1.5 N9  = 1.83400 ν9  =37.2 R15 =  210.50 D15 = 3.0 R16 = (Stop) D16 = Variable R17 =  −58.16D17 = 2.5 N10 = 1.60311 ν10 = 60.7 R18 =  −77.22 D18 = Variable R19 = 177.20 D19 = 4.2 N11 = 1.60311 ν11 = 60.7 R20 =  −42.39 D20 = 1.5 N12 =1.80518 ν12 = 25.4 R21 =  −88.25 D21 = 0.2 R22 =  56.85 D22 = 2.8 N13 =1.51633 ν13 = 64.2 R23 =  218.49 D23 = Variable R24 =  −44.17 D24 = 1.5N14 = 1.77250 ν14 = 49.6 R25 =  51.97 D25 = 3.3 N15 = 1.80518 ν15 = 25.4R26 = 2229.01 Variable Focal Length Separations 76.12 135.00 291.49 D54.00 33.38 59.00 D10 31.30 20.57 2.00 D16 4.00 14.73 33.30 D18 23.8018.20 21.60 D23 22.40 17.35 3.99

|fa/{square root}{square root over (fW·fT)}|=0.275

|foW/frW|=0.335

|foT/frT|=1.068

[0166] According to the invention, the rules of design are set forth asdescribed above. When the shaking of an image is corrected by movingpart of the zoom lens in directions perpendicular to the optical axis, alens unit of small size and light weight is used as the movable lens fordecentering. Moreover, the large shaking of the image can be correctedby a small movement of the decentering lens unit. Further, when thedecentering lens unit is decentered nearly parallel, the produced amountof each of the decentering aberrations described above is small. Thus, azoom lens having the image stabilizing capability and good opticalperformance can be achieved.

[0167] In particular, according to the invention, all decenteringaberrations are well corrected, and a sufficiently large correction isrealized by a sufficiently small decentering movement. The lens unitsother than the lens unit movable for decentering are made to moveaxially to effect zooming. With these, a zoom lens having the imagestabilizing capability which is small in size and light in weight andable to produce an image of high quality can be achieved.

[0168] Next, another embodiment is described where further improvementsare made.

[0169] FIGS. 27(A), 27(B) and 27(C) to FIGS. 29(A), 29(B) and 29(C) arelongitudinal section views of numerical examples 10 to 12 of zoom lensesof the invention. In these drawings, (A) shows the zooming position forthe wide angle end, (B) for a middle focal length, and (C) for thetelephoto end. The zoom lens comprises, from front to rear, a first lensunit L1 of positive refractive power, a second lens unit L2 of negativerefractive power, a third lens unit L3 of positive refractive power anda fourth lens unit L4 of positive refractive power. A stop SP ispositioned on the object side of the third lens unit L2 and arranged onzooming to move in unison with the third lens unit L3. IP stands for animage plane. The third lens unit L3 and the fourth lens unit L4constitute a rear lens unit L_(q). When q zooming from the wide-angleend to the telephoto end, the first lens unit L2, the third lens unit L3and the fourth lens unit L4 move axially toward the object side. Whenthe zoom lens vibrates, the shaking of the image is corrected (the imageis stabilized) by moving the second lens unit L2 as the decentering lensunit in directions perpendicular to the optical axis.

[0170] In the invention, the refractive powers of all the lens units,the refractive power arrangement and other design parameters aredetermined so as to include a wide angle region in which the shortestfocal length fW is shorter than the diagonal length of the image frame.

[0171] In the invention, the focal length f_(p) of the second lens unitsatisfies the following condition:

0.15<|f _(p)/(fw×fT)^(½)<0.50  (9)

[0172] where fW and fT are the shortest and longest focal lengths of theentire system, respectively.

[0173] The inequalities of condition (9) give a range for the ratio ofthe focal length of the second lens unit as the decentering lens unit tothe shortest and longest focal lengths of the entire system. When thelower limit of the condition (9) is exceeded, as this means that thefocal length of the decentering lens unit is too short, a problem arisesin that it becomes difficult to correct the variation of aberrationswith zooming and that the zoom ratio cannot be made high enough. Anotherproblem is that the decentering lens unit cannot be constructed with afew lens elements, being not suited to improve the compact form.

[0174] Conversely when the upper limit of the condition (9) is exceeded,as this means that the focal length of the decentering lens unit is toolong, it is advantageous at correcting various aberrations, but thedecenter sensitivity of the decentering lens unit (the ratio of themovement of the decentering lens unit to the displacement of the image)cannot be made large. For this reason, it becomes necessary to increasethe movement of the decentering lens unit for image stabilization.Another problem arises in that the zooming movement of each of the lensunits increases largely, being not suited to improve the compact form.

[0175] Besides these, in the invention, the second lens unit is madestationary during zooming to thereby facilitate minimization of the sizeof the housing for the zoom lens and its operating mechanism and toassure improvements of the precision accuracy of the mounting mechanismfor the lens system by limiting the probability of occurrence ofinclination of the lens units to a minimum.

[0176] (A) Next, in the invention, in a case where the third lens unitL3 and the fourth lens unit L4 are treated as a rear lens unit having atleast one lens unit, the features are described below.

[0177] (A-1) In the invention, the focal length f_(o) of the first lensunit, the focal length f_(q) for the telephoto end of the rear lens unitand the principal point interval e_(T) for the telephoto end between thefirst and second lens units satisfy the following condition:

0.5<|f _(q)/(f _(o) −e _(T))|<1.2  (10)

[0178] The inequalities of condition (10) are to properly determine eachof the focal lengths of the first lens unit and the rear lens unit whichare positioned before and after the second lens unit as the decenteringlens unit. In particular, on the assumption that the Petzval sum of eachof the lens units is nearly proportional to the refractive power, whenthis condition is satisfied, it is made possible to correct decenteringaberrations well, in other words, to achieve the before-described objectby a simple lens configuration. When the upper or lower limit of thecondition (10) is exceeded, as this means that the refractive powerarrangement over all the lens units is improper, it becomes difficult torealize a zoom lens having the image stabilizing function with thewide-angle region of the compact form. In the condition (10), the lowerlimit may be altered to 0.6, and the upper limit to 1.0. If so, itbecomes easier to realize a zoom lens having a substantially good imagestabilizing function.

[0179] (A-2) The Petzval sums P_(p) and P_(q) of the second lens unitand the rear lens unit, respectively, satisfy the following condition:

1.1<|P _(p) /P _(q)|<1.7  (11)

[0180] The inequalities of condition (11) give a range for the ratio ofthe Petzval sums of the decentering lens unit L2 and the rear lens unitthat directly follows. When the lower limit of the condition (11) isexceeded, as this means that the absolute value of the Petzval sum ofthe decentering lens unit is relatively small, it becomes difficult tocorrect decentering field curvature. Conversely when the upper limit ofthe condition (11) is exceeded, as this means that the absolute value ofthe Petzval sum of the decentering lens unit is relatively large, thePetzval sum of the entire lens system is liable to take a negativevalue. Therefore, it becomes difficult to well correct field curvaturein the non-decentering state.

[0181] Also, in the condition (11), the lower limit may be altered to1.2, and the upper limit to 1.6. If so, it becomes easier to realize asubstantially further improved zoom lens. Also, in the condition (11),the lower limit may be further increased to 1.3 and the upper limit to1.6. If lens materials that satisfy this condition are selected, and therefractive power arrangement is properly determined, it becomes easierto further improve the correction of decentering field curvature.

[0182] (B) In another case where the third lens unit L3 and the fourthlens unit L4 are considered to be independent of each other, theinvention has features described below.

[0183] (B-1) The focal length f_(o) of the first lens unit, the overallfocal length f_(q) for the telephoto end of the third and fourth lensunits and the principal point interval e_(T) for the telephoto endbetween the first and second lens units satisfy the following condition:

0.5<|f _(q)/(f _(o) −e _(T))|<1.2  (10a)

[0184] This condition should be satisfied from a similar reason to thatof the condition (10).

[0185] (B-2) The Petzval sum P_(p) of the second lens unit and the totalsum P_(q) of the Petzval sums of the third and fourth lens units satisfythe following condition:

1.1<|P _(p) /P _(q)|<1.7  (11)

[0186] The inequalities of condition (12) give a range for the ratio ofthe Petzval sum of the decentering lens unit L2 to the Petzval sum ofthe lens units that follow toward the image side, or the third andfourth lens units. When the lower limit of the condition (12) isexceeded, as this means that the absolute value of the Petzval sum ofthe decentering lens unit is relatively small, it becomes difficult tocorrect decentering field curvature. Conversely when the upper limit ofthe condition (12) is exceeded, as this means that the absolute value ofthe Petzval sum of the decentering lens unit is relatively large, thePetzval sum of the entire optical system is liable to take a negativevalue and it becomes difficult to correct field curvature well in thenon-decentering state.

[0187] Also in the condition (12), the lower limit may be altered to 1.2and the upper limit to 1.6. If so, it becomes easier to realize asubstantially improved zoom lens. Also, in the condition (12), the lowerlimit may be further increased to 1.3 and the upper limit to 1.6. Iflens materials which satisfy this condition are selected, and therefractive power arrangement is proper, it becomes easier to wellcorrect decentering aberration.

[0188] As has been described before, an optical system whichaccomplishes the objects of the invention employs the refractive powerarrangement shown in FIG. 26(A).

[0189] Of course, the q-th lens unit described before may be either oneor even divided into a plurality of lens units. The latter is morecommon for realizing a zoom lens well corrected for aberrations.

[0190] So, in the invention, the zoom lens comprises, from front torear, a first lens unit of positive refractive power, a second lens unitof negative refractive power and a rear lens unit comprised of one or aplurality of lens units and having a positive overall refractive power,totaling at least three lens units, wherein the second lens unit ismoved in directions perpendicular to the optical axis when the shakingis corrected.

[0191] Here, the equation (m) is explained again. In the ordinaryphotographic lens, if the object lies at infinity, the initial valuesfor the paraxial light ray can be set as follows:

α_(o)=0  (o)

h_(o)=1  (p)

[0192] Here, using the paraxial ray tracing formula, the followingequations are obtained:

α_(p)=α_(o) +h _(o)ø_(o)=ø_(o)  (q)

h _(p) =h _(o) +e _(o)α_(p)=1−e _(o)ø_(o)  (r)

[0193] where e_(o) is the principal point interval between the first andsecond lens units.

[0194] By inserting the equations (q) and (r) into the equation (m), thefollowing equation is obtained:

(PE)=cø _(p)((1−e _(o)ø_(o))ø_(q)−ø_(o))  (s)

[0195] Therefore, to well correct primary decentering field curvature(PE),

(1/ø_(q))/((1/ø_(o))−e _(o))≈1  (t)

[0196] should be established.

[0197] That is, it is desirable to determine the focal length f_(o) ofthe first lens unit, the focal length f_(q) of the rear lens unit andthe principal point interval e_(o) so as to satisfy the followingrelationship:

f _(q)/(f _(o) −e _(o))≈  (u)

[0198] Though the foregoing has been described on the assumption thatthe Petzval sum of every lens unit is proportional to the refractivepower, it is in the rear lens unit that this proportional relationshipis not always established, depending on the material of the lens and thenumber of constituent lenses. If this proportional relationship isregarded as approximately valid, the equation (u) defines a condition ofcorrecting primary decentering field curvature (PE).

[0199] Based on the consideration described above, the invention isapplied to a type of zoom lens that includes a wide-angle region inwhich the shortest focal length of the entire system is shorter than thediagonal length of the image frame. The zoom lens comprises, from frontto rear, a first lens unit of positive refractive power, a second lensunit of negative refractive power and a rear lens unit comprised of oneor two or more lens units and whose overall refractive power ispositive, totaling at least three lens units, wherein the second lensunit is made to move in directions perpendicular to an optical axis tothereby stabilize the image. Another rule of lens design is set forthfor the foal length f_(o) of the first lens unit, the focal length f_(q)of the rear lens unit and the principal point interval e_(T) between thefirst and second lens units for the telephoto end. When this rule orcondition (10) is satisfied, a zoom lens having an image stabilizingfunction which has solved the subject described before is realized.

[0200] The inequalities of condition (10) has an equivalent significanceto that of the equation (u) described before. Its upper and lower limitsare determined empirically. It should be pointed out that, instead ofthe principal point interval e_(o) in the equation (u), the factor inthe condition (10) uses the principal point interval for the telephotoend. The reason for this is that the decenter sensitivity is higher whenin the telephoto end than when in the wide-angle end and therefore thatthe produced amount of decentering aberrations for an equivalentdecentering movement increases largely with a high possibility when inthe telephoto end. It is, of course, desirable that, even for thewide-angle end, the zoom lens configuration is made likewise to nearlysatisfy the equation (u).

[0201] The invention is still to apply such principles to more specificzoom lenses. In the invention, as the zoom lens having the imagestabilizing function, choice is given mainly to standard zoom lenseswhose range includes from the wide-angle region to the telephoto region.As a model embodying one form of this, the zoom lens is made up,comprising, from front to rear, a first lens unit of positive refractivepower, a second lens unit of negative refractive power, a third lensunit of positive refractive power and a fourth lens unit of positiverefractive power, that is, in the 4-uit form.

[0202] First, as the lens unit which is made to move in directionsperpendicular to the optical axis to stabilize the image, on theassumption that the refractive power arrangement of FIG. 26(A) is used,the second lens unit of negative refractive power is selected. Then, therefractive powers of all the lens units are determined so as to satisfythe condition (10) described before. To allow the decenter sensitivityof the decentering lens unit to become high enough, the refractive powerof the decentering lens unit, too, is determined so as to satisfy thecondition (9). With these in mind, a fundamental framework for the zoomlens having the image stabilizing function is realized.

[0203] To further improve the correction of decentering aberrations,particularly decentering curvature of field, produced when thedecentering lens unit is decentered, it becomes necessary to morerigorously reduce the decentering field curvature (PE) expressed by theequation (g) described before. In the equation (g), α_(p) and α_(p)′ arethe reduced angles of inclination of the paraxial light rays and theirvalues are determined roughly depending on the refractive powerarrangement over all the lens units. What refractive power arrangementto select for the given lens units suffers some degrees of limitationunder the condition that the zoom lens should be realized to asufficiently compact form and, therefore, cannot be altered much freely.Also, P_(p) and P_(q) are the Petzval sums of the decentering lens unitand that lens unit which is positioned on the image side thereof,depending roughly on the refractive powers of the lens units, but arepossible to vary to some extent by appropriately altering the number oflens elements in each of the lens units and the materials from which thelens elements are made up.

[0204] So, with the zoom lens having such a refractive powerarrangement, that is, the reduced angles of inclination α_(p) and α_(p)′of the paraxial light rays, when to further improve the correction ofdecentering aberrations, particularly field curvature, produced when thedecentering lens unit is decentered, it becomes necessary to properlydetermine the values of the Petzval sums P_(p) and P_(q) of the lensunits.

[0205] The condition (11) is set forth for the zoom lens having such arefractive power arrangement and has a range determined based on theconsideration described above. When this condition is satisfied, thePetzval sums of the lens units takes proper values. In actual practice,there is a case where even when the Petzval sums P_(p) and P_(q) aredetermined so as to satisfy the condition (11), the equation (g)described above cannot be put to “0”. However, to realize a zoom lenshaving the image stabilizing function to a compact form as a whole, itis desirable to satisfy the condition (11).

[0206] Next, numerical examples 10 to 12 of the invention are shown. Inthe numerical data for the examples 10 to 12, Ri is the radius ofcurvature of the i-th lens surface, when counted from the object side,Di is the i-th axial thickness or air separation, when counted from theobject side and Ni and νi are respectively the refractive index and Abbenumber of the glass of the i-th lens element, when counted from theobject side.

NUMERICAL EXAMPLE 10

[0207] f = 35.60 − 101.97 Fno. = 3.60 − 4.60 R1  =   220.00 D1  = 2.5N1  = 1.80518 ν1  = 25.4 R2  =    61.24 D2  = 8.0 N2  = 1.51633 ν2  =64.2 R3  = −134.30 D3  = 0.2 R4  =    37.37 D4  = 4.8 N3  = 1.69680 ν3 = 55.5 R5  =    91.27 D5  = Variable R6  =    57.75 D6  = 1.5 N4  =1.69680 ν4  = 55.5 R7  =    14.23 D7  = 4.4 R8  =  −46.08 D8  = 1.2 N5 = 1.69680 ν5  = 55.5 R9  =    33.37 D9  = 1.0 R10 =    26.83 D10 = 2.9N6  = 1.84666 ν6  = 23.8 R11 = −323.36 D11 = 1.5 R12 =  −23.12 D12 = 1.2N7  = 1.77250 ν7  = 49.6 R13 =  −48.97 D13 = Variable R14 = (Stop) D14 =1.0 R15 =    30.87 D15 = 3.7 N8  = 1.51633 ν8  = 64.2 R16 =  −45.12 D16= 0.2 R17 =    31.86 D17 = 5.2 N9  = 1.51633 ν9  = 64.2 R18 =  −16.35D18 = 1.2 N10 = 1.83400 ν10 = 37.2 R19 =   202.89 D19 = Variable R20 = −53.43 D20 = 3.3 N11 = 1.60311 ν11 = 60.7 R21 =  −19.10 D21 = 0.2 R22 =   56.40 D22 = 3.0 N12 = 1.65160 ν12 = 58.5 R23 =  −78.57 D23 = 5.2 R24=  −18.51 D24 = 1.5 N13 = 1.80610 ν13 = 41.0 R25 =  −72.51 VariableFocal Length Separations 35.60 70.00 101.97 D5 2.50 17.66 24.50 D1314.50 6.34 1.50 D19 9.30 7.80 8.10

[0208] Diagonal Length of Image Frame: 43.27

f_(o)=70.02

f_(p)=−17.07

f_(q)=26.76

f_(T)=31.64

|f _(q)/(f _(o) −e _(T))|=0.697

|f _(p)/(fW·fT)^(½)|=0.283

|P _(p) /P _(q)|=1.286

NUMERICAL EXAMPLE 11

[0209] f = 35.97 − 101.72 Fno. = 4.40 − 4.80 R1  =   107.93 D1  = 2.5N1  = 1.80518 ν1  = 25.4 R2  =    48.11 D2  = 7.6 N2  = 1.51633 ν2  =64.2 R3  = −583.75 D3  = 0.2 R4  =    34.64 D4  = 5.9 N3  = 1.51633 ν3 = 64.2 R5  =   289.32 D5  = Variable R6  =   153.82 D6  = 1.5 N4  =1.69680 ν4  = 55.5 R7  =    15.13 D7  = 5.2 R8  =  −64.57 D8  = 1.2 N5 = 1.69680 ν5  = 55.5 R9  =    46.43 D9  = 0.5 R10 =    26.72 D10 = 3.2N6  = 1.84666 ν6  = 23.8 R11 =   351.36 D11 = 2.0 R12 =  −25.55 D12 =1.2 N7  = 1.69680 ν7  = 55.5 R13 =  −47.49 D13 = Variable R14 = (Stop)D14 = 1.0 R15 =    27.73 D15 = 2.9 N8  = 1.69680 ν8  = 55.5 R16 = −58.49 D16 = 0.2 R17 =    35.28 D17 = 3.7 N9  = 1.51633 ν9  = 64.2 R18=  −18.24 D18 = 1.2 N10 = 1.83400 ν10 = 37.2 R19 =    59.60 D19 =Variable R20 =  −79.17 D20 = 3.0 N11 = 1.69680 ν11 = 55.5 R21 =  −18.24D21 = 0.2 R22 =    41.35 D22 = 2.8 N12 = 1.60311 ν12 = 60.7 R23 =−142.91 D23 = 2.0 R24 =  −18.21 D24 = 1.2 N13 = 1.74400 ν13 = 44.8 R25 =  279.13 Variable Focal Length Separations 35.97 70.00 101.72 D5 2.0011.80 17.70 D13 19.50 7.60 1.50 D19 9.30 8.18 8.84

[0210] Diagonal Length of Image Frame: 43.27

f_(o)=65.01

f_(p)=−18.99

f_(q)=28.96

f_(T)=25.55

|f _(q)/(f _(o) −e _(T))|=0.734

|f _(p)/(fW·fT)^(½)|=0.314

|P _(p) /P _(q)|=1.472

NUMERICAL EXAMPLE 12

[0211] f = 36.11 − 102.00 Fno. = 3.60 − 4.60 R1  =   133.94 D1  = 2.6N1  = 1.80518 ν1  = 25.4 R2  =    59.61 D2  = 7.9 N2  = 1.60311 ν2  =60.7 R3  = −524.63 D3  = 0.2 R4  =    43.75 D4  = 6.1 N3  = 1.51633 ν3 = 64.2 R5  =   168.13 D5  = Variable R6  =    86.79 D6  = 1.5 N4  =1.80400 ν4  = 46.6 R7  =    15.28 D7  = 5.0 R8  =  −36.46 D8  = 1.2 N5 = 1.80400 ν5  = 46.4 R9  =    93.00 D9  = 0.5 R10 =    31.16 D10 = 3.8N6  = 1.80518 ν6  = 25.4 R11 =  −38.98 D11 = 1.0 R12 =  −26.75 D12 = 1.3N7  = 1.80400 ν7  = 46.6 R13 = −303.98 D13 = Variable R14 = (Stop) D14 =1.5 R15 =    32.69 D15 = 3.8 N8  = 1.69680 ν8  = 55.5 R16 =  −48.79 D16= 0.2 R17 =    30.11 D17 = 2.7 N9  = 1.51633 ν9  = 64.2 R18 =   128.84D18 = 2.4 R19 =  −23.20 D19 = 9.5 N10 = 1.80518 ν10 = 25.4 R20 =  107.11 D20 = 1.0 R21 = −195.04 D21 = 3.4 N11 = 1.51742 ν11 = 52.4 R22=  −20.35 D22 = Variable R23 =    48.8 D23 = 4.4 N12 = 1.56732 ν12 =42.8 R24 =  −28.31 D24 = 3.0 R25 =  −24.34 D25 = 1.6 N13 = 1.83400 ν13 =37.2 R26 =  −39.82 D26 = 2.0 R27 =  −19.38 D27 = 1.8 N14 = 1.83400 ν14 =37.2 R28 =  −35.59 Variable Focal Length Separations 36.11 70.00 102.00D5 2.00 20.54 28.40 D13 13.80 6.16 1.50 D19 5.80 2.99 2.44

[0212] Diagonal Length of Image Frame: 43.27

f_(o=)80.00

f_(p)=−17.62

f_(q)=27.76

f _(T)=37.41

|f _(q)/(f _(o) −e _(T))|=0.652

|f _(p)/(fW·fT)^(½)|=0.290

|P _(p) /P _(q)|=1.296

[0213] According to the invention, as described above, part of theoptical system, or one lens unit, is made to move in directionsperpendicular to an optical axis when the shaking of an image iscorrected. Along with this, each lens element is properly arranged toassist in well correcting all decentering aberrations. In addition, itis realized that a sufficiently short decentering movement suffices forcorrecting the sufficiently large shaking of the image, therebyimproving the compact form of the instrument as a whole. Hence, it ispossible to achieve a zoom lens having the image stabilizing functionsuited to the standard zoom lens whose range includes from a wide-angleregion to the standard region.

What is claimed is:
 1. A zoom lens comprising, from front to rear, afirst lens unit of positive refractive power, a second lens unit ofnegative refractive power, a third lens unit of positive refractivepower, a fourth lens unit of negative refractive power, a fifth lensunit of positive refractive power and a sixth lens unit of negativerefractive power, zooming being performed by varying the separationsbetween said lens units, and said zoom lens satisfying the followingcondition: 0.3<|f4/fT|<10.0 where f4 is the focal length of said fourthlens unit and fT is the longest focal length of the entire system.
 2. Azoom lens according to claim 1, satisfying the following conditions:0.1<|f2/fT|<0.18 0.12<|f6/fT|<0.3 where f2 and f6 are the focal lengthsof said second lens unit and said sixth lens unit, respectively.
 3. Azoom lens according to claim 1 or 2, wherein at least one of said secondlens unit and said fourth lens unit remains stationary during zooming.4. A zoom lens according to claim 1 or 2, wherein said fourth lens unitincludes a negative lens of meniscus form convex toward an image side.5. A zoom lens according to claim 1, wherein letting the separationsbetween the i-th and (i+1)st lens units for a wide-angle end and atelephoto end be denoted by DiW and DiT, respectively, the followingconditions are satisfied: D1W<D1T D2W>D2T D3W<D3T D4W>D4T D5W>D5T
 6. Azoom lens comprising, from front to rear, a first lens unit of positiverefractive power, a second lens unit of negative refractive power, athird lens unit of positive refractive power, a fourth lens unit ofnegative refractive power, a fifth lens unit of positive refractivepower and a sixth lens unit of negative refractive power, zooming beingperformed by varying the separations between said lens units, and saidzoom lens satisfying the following condition: 0.3<ln Z ₂ /ln Z<1 wherein represents natural logarithm, Z₂ is a zoom ratio of said second lensunit in zooming from a wide-angle end to a telephoto end, and Z is azoom ratio of the entire system.
 7. A zoom lens according to claim 6,satisfying the following condition: 0.5<{square root}{square root over(f1/fW fT)}<3.0 where f1 is the focal length of said first lens unit andfW and fT are the shortest and longest focal lengths of the entiresystem, respectively.
 8. A zoom lens according to claim 6, wherein atleast one of said second, said fourth and said sixth lens units remainsstationary during zooming.
 9. A zoom lens according to claim 6, whereinletting the separation between the i-th and (i+1)st lens units for awide-angle end and a telephoto end be denoted by DiW and DiT,respectively, the following conditions are satisfied: D1W<D1T D2W>D2TD3W<D3T D4W>D4T D5W>D5T
 10. A zoom lens having an image stabilizingfunction, comprising at least one lens unit positioned on each of theobject side and image side of a lens unit which is stationary duringzooming and arranged to move axially during zooming, wherein said lensunit which is stationary during zooming is made to move in directionssubstantially perpendicular to an optical axis so as to correct shakingof an image.
 11. A zoom lens having an image stabilizing function,comprising, from front to rear, a first lens unit of positive refractivepower axially movable for zooming, a second lens unit of negativerefractive power stationary during zooming, a rear lens unit includingat least one lens unit, whose overall refractive power is positive andaxially movable for zooming, wherein said second lens unit is made tomove in directions substantially perpendicular to an optical axis so asto correct shaking of an image.
 12. A zoom lens having an imagestabilizing function according to claim 10, satisfying the followingcondition: 0.15<|fa/{square root}{square root over (fW·fT)}|<0.5 wherefa is the focal length of said lens unit which is stationary duringzooming, and fW and fT are the shortest and longest focal lengths of theentire system, respectively.
 13. A zoom lens having an image stabilizingfunction according to claim 10, satisfying the following conditions:0.20<|foW/frW|<1.50 0.80<|foT/frT|<6.0 where foW and foT are the overallfocal lengths for a wide-angle end and a telephoto end of those lensunits which are positioned on the object side of said stationary lensunit, respectively, and frW and frT are the overall focal lengths forthe wide-angle end and the telephoto end of said stationary lens unitand those lens units which are positioned on the object side of saidstationary lens unit, respectively.
 14. A zoom lens having an imagestabilizing function, comprising, from front to rear, a first lens unitof positive refractive power, a second lens unit of negative refractivepower, a third lens unit of positive refractive power, a fourth lensunit of positive refractive power and a fifth lens unit of negativerefractive power, said second lens unit being made stationary duringzooming, and zooming being performed by varying the separations betweensaid lens units, wherein said second lens unit is made to move indirections substantially perpendicular to an optical axis so as tocorrect shaking of an image.
 15. A zoom lens having an image stabilizingfunction according to claim 14, wherein, during zooming from awide-angle end to a telephoto end, letting the separations for thewide-angle end and the telephoto end between the i-th and (i+1)st lensunits be denoted by DiW and DiT, respetively, said lens units are movedin such relation as to satisfy the following conditions: D1W<D1T D2W>D2TD4W>D4T
 16. A zoom lens having an image stabilizing function,comprising, from front to rear, a first lens unit of positive refractivepower, a second lens unit of negative refractive power, a third lensunit of positive refractive power, a fourth lens unit of negativerefractive power, a fifth lens unit of positive refractive power and asixth lens unit of negative refractive power, said second lens unitbeing stationary during zooming, and zooming being performed by varyingthe separations between said lens units, wherein said second lens unitis made to move in directions substantially perpendicular to an opticalaxis so as to correct shaking of an image.
 17. A zoom lens having animage stabilizing function according to claim 16, wherein, duringzooming from a wide-angle end to a telephoto end, letting theseparations between the i-th and (i+1)st lens units for the wide-angleend and the telephoto end be denoted by DiW and DiT, respectively, saidlens units are made to move in such relation as to satisfy the followingconditions: D1W<D1T D2W>D2T D3W<D3T D5W>D5T
 18. A zoom lens having animage stabilizing function according to claim 14 or 16, satisfying thefollowing condition: 0.15<|fa/{square root}{square root over(fW·fT)}|<0.5 where fa is the focal length of said second lens unit, andfW and fT are the shortest and longest focal lengths of the entiresystem, respectively.
 19. A zoom lens having an image stabilizingfunction, comprising, from front to rear, a first lens unit of positiverefractive power, a second lens unit of negative refractive power and arear lens unit including at least one lens unit and having a positiveoverall refractive power, zooming from a wide-angle end to a telephotoend being performed by axially moving said first lens unit and at leastone lens unit in said rear lens unit toward an object side, and theshortest focal length of the entire system being sorter than thediagonal length of an image frame, wherein said second lens unit is madeto move in directions perpendicular to an optical axis so as to correctshaking of an image occurring when said zoom lens vibrates.
 20. A zoomlens having an image stabilizing function according to claim 19,satisfying the following condition: 0.5<|f _(q)/(f _(o) −e _(T))|<1.2where f_(o) is the focal length of said first lens unit, f_(q) is thefocal length for the telephoto end of said re ar lens unit, and e_(T) isthe principal point interval between said first lens unit and saidsecond lens unit for the telephoto end.
 21. A zoom lens having an imagestabilizing function according to claim 19, satisfying the followingcondition: 1.1<|P _(p) /P _(q)|<1.7 where P_(p) and P_(q) are thePetzval sums of said second lens unit and said rear lens unit,respectively.
 22. A zoom lens having an image stabilizing function,comprising, from front to rear, a first lens unit of positive refractivepower, a second lens unit of negative refractive power, a third lensunit of positive refractive power and a fourth lens unit of positiverefractive power, zooming being performed by varying the separationsbetween said lens units, wherein said second lens unit is made to movein directions perpendicular to an optical axis so as to correct shakingof an image occurring when said zoom lens vibrates.
 23. A zoom lenshaving an image stabilizing function according to claim 22, satisfyingthe following condition: 0.5<|f _(q)/(f _(o) −e _(T))|<1.2 where f_(o)is the focal length of said first lens unit, f_(q) is the overallrefractive power of said third lens unit and said fourth lens unit for atelephoto end, and e_(T) is the principal point interval between saidfirst lens unit and said second lens unit for the telephoto end.
 24. Azoom lens having an image stabilizing function according to claim 22,satisfying the following condition: 1.1<|P _(p) /P _(q)|<1.7 where P_(p)is the Petzval sum of said second lens unit and P_(q) is the total sumof the Petzval sums of said third lens unit and said fourth lens unit.25. A zoom lens having an image stabilizing function according to claim19, satisfying the following condition: 0.15<|f _(p)/(fw×fT)^(½)<0.50where f_(p) is the focal length of said second lens unit and fW and fTare the shortest and longest focal lengths of the entire system,respectively.
 26. A zoom lens having an image stabilizing functionaccording to claim 19, wherein said second lens unit is made stationaryduring zooming.